Popular Science Monthly/Volume 68/March 1906/The Physiography of the Adirondacks
|THE PHYSIOGRAPHY OF THE ADIRONDACKS|
Introduction.—The state of New York is shaped like a shoe, with its toe pointing due west and a long spur extending from the heel to the east. In the upper part of the shoe where the ankle of the wearer would be placed, is the Adirondack region, containing 10,000 square miles of very sparsely inhabited mountain, plateau and forest. It embraces the highest summits in the state, and at the same time the highest in eastern North America, except the White Mountains of New Hampshire and the Blue Ridge of North Carolina. Were it not for these two, even though the Appalachian region is decidedly and impressively mountainous, the Adirondacks would remain the loftiest summits in the east; and the equal of Mt. Marcy, called Tahawus or the 'Cloud-splitter' by the Indians, would not appear on the hither side of the Black Hills of South Dakota or the remoter Rocky Mountains.
Geological Formations Present.—The Adirondack region in its geology presents an important and interesting series of Precambrian rocks. Roughly speaking, nearly the whole area consists of gneisses, but the metamorphic rocks can be separated into a great series of sedimentary gneisses, quartzites and coarsely crystalline limestones, on the one hand, and, on the other, into a second great series of eruptive syenites, granites and rocks of the gabbro family. Except for the limestones, all these rocks are hard and resistant, their weak points of attack being in a small degree their schistosity, and in a greater degree their joints and faults.
On all sides the Precambrian rocks are mantled with the Paleozoics, the oldest of which is the Potsdam sandstone of the Upper Cambrian, a hard quartzite, gray, pink and pale yellow in color. The latest member of the Paleozoics having any association with the old crystallines is the Utica slate, near the top of the Ordovician, while between the Potsdam and the Utica appear in order from below, upward, the Beekmantown, Chazy and Trenton limestones. Except perhaps the Utica slate and the Trenton limestone, which is somewhat shaly, all these are firm, resistant rocks. The visible contacts of the Paleozoic strata with the old crystallines, especially on the northwest and west, are often those of sedimentary overlap, due to an advancing shore line, but on the east and northeast they are much more frequently due to block-faulting of a most interesting character and exceedingly significant as throwing light on the physiography of the interior mountains. Aside from this, however, the Paleozoic strata enter only in a very minor way
into the structure of the mountains. They occur around the edges, except for a few isolated outliers from five to forty miles within the Precambrian area.
After the deposition of the Utica, so far as the actual evidence is concerned, there were no more rocks laid down until the advent of the Labradorean ice sheet of the Glacial epoch. Whether later Paleozoics once existed and have been removed by erosion, or whether the area has been continuously land from the close of the Ordovician to the present, may be esteemed to a certain extent open to debate. From observations near Little Falls on the southern side, Professor H. P. Gushing has concluded that the Niagara limestone probably extended a long distance into the area of the crystallines if not entirely across. But no trace of it has been discovered in place, and the great gap in time from the Ordovician to the Glacial epoch must be interpreted, if at all, by the structural and physiographic records. The Labradorean ice sheet was, however, of enormous importance. Its deposits are heavy, and it doubtless operated to form numberless lakes and to greatly reorganize the drainage, as will be later pointed out in a few suggestive instances.
The Mountains Proper and the Western Plateau.—The Adirondack region, sometimes referred to as the Great North Woods, is mountainous in its eastern half, and has its highest peaks near its center, but on the west the mountains disappear and the area becomes a plateau ranging from 2,000 feet above tide gradually downward to the west until it is but slightly higher than Lake Ontario and the St. Lawrence. The
loftiest peak is Marcy, 5,344 feet, and there are one or two others which exceed 5,000, together with five or six additional above 4,500, and many above 3.000. The mountains are ranged in visible northeast and southwest lines, and are often very steep if not positively precipitous in the portions that look to the southeast or northwest. There are also other steep faces nearly at right angles with the above, but they are less pronounced. When viewed from a distance the profile is strongly serrate—a gradual slope up on one side being cut off abruptly by an almost vertical descent on the other.The individual mountains are diversified in shape. Mt. Marcy is a very low cone, and the last stages of its ascent are very much like climbing a dome. Mt. McIntyre has a gradual slope from the northwest,
but a precipitous escarpment on the southeast. The Gothics are like a steep wedge standing on its base, and tapering from all four sides of the base to the ridge. Whiteface is a long sharp ridge, steep if not actually precipitous on each side, and leading up to a peak at the southwestern end. Some buttresses run out from the ridge and make beautiful cirques on its flanks. Hurricane, when viewed from the east, resembles a sharp volcanic cone; from the west it is flat. There are several, of which Dix is the highest example, which, like Vesuvius, have a small conical summit set upon a large mountainous base. Nipple-top is a rather favorite name in the local nomenclature of the inhabitants. There are several smaller mountains which have the outlines of a steep haystack when viewed from certain directions, and their precipitous sides and doming tops fix the eye at once. Yet they may each be a ridge when seen from the opposite. One very exceptional peak, quite inappropriately called Sugarloaf, near Hulett's on Lake George, is a circular mesa, with a flat top several acres in area and dropping with steep sides to the lake slope below. It resembles a round fort or old-time castle, such as St. Angelo, across the Tiber from Rome, or Castle William on Governor's Island in New York Harbor. It is due to flat foliation in the gneisses combined with intersecting vertical joints. Not a few other mountains, although of very irregular shapes at the base, yet have flat tops of considerable area. Their level summits appear to be the surviving remnants of some old-time peneplain now faulted into relief, as will be later explained.
The plateau portion, which makes up practically the western half, is not absolutely flat, but is more or less diversified with low hills and intervening broad valleys. Occasional summits give views of moderate extent, but no elevations can properly be called mountains, and the general term plateau is most expressive. It may well be the remnant of an old peneplain, perhaps the important one widely developed in Cretaceous time in the east.
The Valleys.—The mountains can not all be described without parallel and complementary reference to the valleys, and in discussing the latter the causes which have led to the production of the former may best be mentioned.At least two marked and contrasted types of valleys may be distinguished. There is an old series which in part probably dates back even to Precambrian time. In the eastern mountains the cause of their excavation is oftentimes obviously the presence of relatively soft and easily eroded limestone in the series of gneisses. In several notable cases the Potsdam and even later Paleozoic formations can be traced by the remaining outliers some miles into the old crystallines, and although subsequent faulting has exercised its modifying and disguising influence, yet it has appeared to several observers that the old
depressions were recognizable. The old valleys have gentle slopes and wide expanses. Their contours are softened down and the whole physiographic expression is one which suggests long-continued erosion and maturity of form. In studying out these relations, one has also to eliminate as far as possible the mask of glacial drift which is everywhere in evidence. The valleys of the old system run in their most marked development east and west, and north and south. Several of them are occupied to-day by some of the largest streams and lakes—such as Schroon lake, the southern third of Lake George, parts of the Hudson Valley and several tributary to Lake Champlain. One half of an old valley will often remain with characteristically gentle slope and mild topography, while the other half of the depression will consist of the steep precipices of the next type. And as the second type has been superimposed upon the first, the observer is often forced to trace the former out despite its disguises and modifications.
The second type of valley is obviously the result of faulting, and of faulting that is of no great geological antiquity. The sides and steep escarpments and the depressions may have all the characteristics of a 'Graben-senkung,' or of a fjord, if the latter can be imagined away from the sea. In the southeastern portion of the mountains as well as in the interior, three pronounced sets of fault escarpments may be recognized and plotted. The most marked one is northeast, and to it is due the general northeast and southwest trend of the mountains. The topographic maps, and still more the relief model prepared by E. A. Howell, show this in all desirable clearness. Along the shores of Lake Champlain the ridges come in one after another from the southwest, making the western shore of the lake a series of bays with bold intervening headlands. The central portion of Lake George, where the wildest and most picturesque scenery is found, is another example. Precipitous escarpments characterize the shores, while mountains of rugged outline shut in the observer. In the interior these characters appear on an even grander scale. The Lower Ausable lake is a Graben; Avalanche lake, one of the sources of the Hudson, has cliffs so steep that the traveler must take to a boat to find a passage. In Wilmington notch, as also in Indian pass, cliffs hardly less than a thousand feet, front the traveler.
A second but less strongly developed series of faults runs northwest and southeast and is the cause of many cross breaks at right angles with the set last mentioned. They serve to block out the individual mountains amid the general northeast trend of the ridges, and are responsible for innumerable little cross-passes which are found on all the summits. In the high mountains, the little cross-passes almost always have a well-defined bear or deer trail following them through. They serve also to develop sharp shoulders in the precipices of the first type and to give the shores of a lake a very serrated outline. In the Mount Marcy and Elizabethtown quadrangle they, with the first set, have occasioned the interesting 'lattice-shaped' drainage noted by Professor Brigham some years ago. The little streams flow
Fig. 8. Deer's Leap, an Escarpment on Lake George—produced by intersecting northeast and northwest joints, or perhaps faults—and much freshened by the ice of the Glacial epoch.
down moderate slopes from the northwest, against high and sparsely wooded precipices on the southeast and join larger streams which flow northeast or southwest. When a wide area is studied, it is only the older and still surviving east and west or north and south valleys which break up this lattice-like regularity.
In less frequent occurrence than the northeast and northwest fault breaks, minor ones ranging nearly due north may be recognized—but they do not exercise so important an influence on the general relief.
The three systems of faults have in some instances led to great single precipitous escarpments suggesting that the movement was chiefly confined to one single plane, but it is much more common to find the fault a compound one. That is, a very steep mountain face will consist of a series of small escarpments, each with a bench at its foot. These benches make terraces, and on Lake George one can easily see, even when the mountain is thickly forested, that the trees are growing in pronounced rows with thinner lines of vegetation between. A mountainside may thus look like a gigantic series of furrows, as is true of the ridge from Black Mountain to Elephant Mountain. Where the faults cut across a projecting shoulder the terraces go up one side and down the other like a series of lunettes. Forest fires and the lumberman's axe, while destroying much of the beauty, have yet brought out these features with striking emphasis, and when the light intensifies the relief with shadows they appeal to the observer in the strongest way. The narrow ridge between Lake George and Lake Champlain contains some of the roughest country in all the Adirondack region.
The faults and their escarpments were doubtless much freshened up by the Labradorean ice-sheet which plucked away from their faces the loose rock, sheeted by the parallel faults. In this way the relief was heightened during the Glacial epoch, and its freshness and youth still remain to us, but the faults preceded the ice and were the great governing factors. Thus far no evidence of post-glacial faulting has been observed.
On the south side of the mountains the faults run out in a striking way into the overlapping Paleozoic areas and have been traced as much as thirty or forty miles. One famous one causes the Precambrian rocks on the west to abut sharply for thirty miles against the Cambrian and Ordovician strata, forming an escarpment which faces east. After the Precambrians have disappeared below the Paleozoics for two miles, they rise again into view at the pass called the 'Needles,' where the Mohawk river, the Erie Canal and the New York Central and West Shore Railways find a way close together fifty miles west of Albany. Another is responsible for the Precambrian outlier of Little Falls, recently described by Professor H. P. Cushing. The displacements exhibited in these easily recognized and contrasted strata are of great significance when taken as illuminating the more obscure relations of the Precambrians of the interior mountains.
One interesting corollary of the great northeast and southwest breaks is that a series of basaltic dikes which are widely distributed, which followed the metamorphism of the Precambrian rocks, but which preceded the Potsdam, almost always come up through them and suggest that the breaks go far enough down to have tapped off a reservoir of basic rocks.
The Drainage.—The waters from the Adirondacks flow into both the Hudson and the St. Lawrence Rivers. On the south and southwest they either go directly to the former which rises in their very center;
A fault—escarpment faces the observer.
or else they pass first through the Mohawk. On the north and east, the waters reach the St. Lawrence viâ Lakes George and Champlain, and on the northwest viâ Lake Ontario or directly to the great river itself. The drainage of the high mountains, however, goes almost entirely to the Hudson or to Lake Champlain.
The chief rivers actually in the area are the Hudson and its principal tributary north of Waterford, the Sacondaga, both of which will be shortly described in greater detail; West Canada Creek, and minor tributaries of the Mohawk; the Black, flowing into Lake Ontario; the Oswegatchie, Grass, Raquette, and Salmon-Chateaugay, which pass directly into the St. Lawrence; and the Saranac, Ausable and the outlet of Lake George directly into Lake Champlain. Some of these are largely, if not essentially, preglacial in their courses, occupying the earlier valleys mentioned above. Others have been obviously influenced in their present locations by the glacial deposits. It is clear from the insuperable rocky obstacles presented that drainage must even in the preglacial period have radiated from the central height of land, and that there is a marked preglacial divide around Mt. Marcy which at this time separated the waters going north from those going south. But there are some strange features about the present courses of the Hudson and Sacondaga and some interesting points about Lake George which will be briefly noted.
Fig. 10. A Fault in Paleozoic Strata near Essex, N. Y., on Lake Champlain. The Utica slates, from flatness on the left beyond the picture, are dragged to a fairly steep inclination, where faulted against the hard Beekmantown limestone, which lies several hundred feet below in the stratigraphic series.
open and swampy area to the southwest and directly in the line of its previous courses. It is apparently a case of reversed drainage. After a somewhat sinuous easterly course of eight or ten miles, the Hudson turns again abruptly south, receiving at the same time the Boreas River, which comes in from the north with the waters of a broad, open region much masked by drift and filled with swamps and lakes. It would seem as if the Hudson had jumped thus from one older drainage line to another. The Hudson next flows due south for four or five miles, then turns once more eastward, for eight miles, then south and southeast until it again turns eastward, northward and finally eastward with marked meanders across the great sandy plain near Glens Falls. Finally at Sandy Hill it swings around once more to the south and takes its nearly uniform course for the sea.
The Sacondaga River has also this same peculiar rectangular bending from north and south to east and west courses, and with a most peculiar turn parallel in all respects to the bend of the Hudson, it swings into the latter some miles above Glens Falls.
These bendings are in large part to be explained by the old series of east and west and north and south valleys and by the rearrangements of the older drainage by the glacial drift. When the streams sought to occupy their old north and south channels on the retreat of the ice they seem to have been forced in instances by newly acquired barriers to run in an easterly direction across old but low divides and then to utilize parallel north and south lines of drainage.
Lakes.—The Adirondack region, like all the recently glaciated country, teems with lakes which can he observed in all stages from those of large size like Champlain, George and Schroon, through smaller ones, to those little more than a morass, and finally to cultivated meadow land upon the abandoned bottoms of departed ones whose deltas and terraces stand out clearly. Lake Champlain is the largest and has a total length of 150 miles. It has been recently studied in detail by Professor J. B. Woodworth. It is obviously an old river valley, probably modified somewhat by recent faulting and ponded by some barrier of recent formation at the north. Lake George is next in size and is apparently compounded of two earlier valleys, whose divide
was near the Hundred Islands about midway of its length. One old valley headed up in Northwest Bay, and the other probably did not come much south of Sabbath Day Point. Faulting connected them, however, and the damming by the drift of the old outlet to the south at the head of Kattskill Bay and of the normal outlet to the north into the Trout Brook Valley or possibly eastward into Lake Champlain at Blairs bay, produced the present composite lake, with its precipitous mountainsides and wild rugged scenery. The old relations are greatly obscured by the glacial drift. Schroon Lake is another ponded and drowned river valley, with both a sluggish outlet and a sluggish inlet, the former with wonderfully developed terraces on either side, running like railway embankments as they mark old periods of high water. The other notable series of lakes, like the Fulton Chain, have been produced by the drift in the old valleys, which were the great drainage lines before the glacial epoch. With moderate portages they can be navigated long distances.
Some of the smaller lakes are in fault valleys and not infrequently are on the divides so as to be the sources of the streams. The Cascade lakes (Fig. 7) between the Keene Valley and Lake Placid are good illustrations. Although now two, they were once continuous and have evidently been divided by a landslide.
The Ice Invasion of the Glacial Epoch.—Coming after so long an interval during which the Adirondack area was land the Labradorean ice sheet possesses exceptional interest. All the scratches so far observed and recorded point to a source on the northeast. The glacier advanced from this quarter, and, as has been shown in some detail by Dr. I. H. Ogilvie, rode over the highest mountains and apparently filled the valleys with stagnant ice, since, except in the borders, scratches are rare. In fact the Paleozoic strata, in the lower confines, where the Champlain clays soon buried and preserved the scratches, are the most prolific sources of observations. The hard Precambrian rocks have mostly lost them by weathering.
The ice sheet must have found the Adirondacks covered with a heavy mantle of the products of decomposition. The long time during which the mountains had been land could have had no other result than this. It also found them of rugged topography much as now, because if we believe or assume, as is reasonable, that the Cretaceous peneplain was broken up into the flat-topped blocks by the preglacial faulting, the region must have presented a very irregular barrier in the pathway of the ice. The ice has left not a few characteristic topographic forms as the result of its action. Cirques appear on the flanks of several of the higher mountains, as, for example, on the northwestern side of Giant and the eastern side of Whiteface. Projections of the ridge run out in each case at right-angles to the main axis, affording a depression which must have had its own small glacier on the waning of the ice. This small glacier has eaten back against the main ridge so as to leave the characteristic cirque with its precipitous head.
Near Mt. Marcy, in the Paradox Lake quadrangle, Dr. Ogilvie has noted very perfect and striking cases of small rock basins, which the writer has seen under her guidance. Each is occupied by a small mountain lake, and is a bowl produced by plucking and scoring. Giant kettles or potholes are to be seen in many places around the northern shores of Lake George, and more particularly two or three miles north of Hague, where they are locally called Indian Kettles. There must have been sinkholes in the ice sheet at these points, which are now above the level of the lake, and torrents poured into them until the moulin or mill was established.
While moraines and huge transported boulders are not altogether lacking, yet they favor special localities and, generally speaking, the boulders are of but moderate size. The Potsdam sandstone furnishes a material of special interest, since it can be easily recognized, can be referred to its parent ledges and is found all over the mountain tops.
The larger boulders are a quite marked feature to the west of Schroon Lake Post Office, and from a distance resemble small houses. One now cleft in twain near Hague, on Lake George, is fully thirty feet in diameter (Fig. 13). With the waning and retreat of the ice, lakes were impounded in not a few of the valleys and their surfaces reached to altitudes high above the present bottoms. Near Elizabethtown in the valley of the Boquet River, and in the Keene Valley along the east branch of the Ausable River the deltas formed by tributary streams are still very clearly preserved, cut in two as is usual by the downward erosion of the present stream. Ice must have largely formed the barriers. Other and usually small lakes, as has been noted by Professor C. H. Smyth, Jr., have reached the state of morasses or meadows, affording the so-called vlies of the early Dutch settlers.
With the waning of the great ice sheet the vegetation crept northward, covering moraines, sand-plains and hills with a coat of green. At first obviously Arctic in character as the little colonies of hardy plants still holding out on the mountain tops show, the flora and silva assumed gradually a more temperate aspect and prepared the Great North Woods to be the chief recreation ground for the people of New York and neighboring states.