ONTOLOGY OORT 641 ping southwardly from the N. shore. A marked feature in the topography of the S. shore is the " Lake ridge," a narrow elevation ranging from Sodus in Wayne co. to the Niagara river, nearly parallel with the edge of the lake, and at a distance of from 3 to 8 m. from it. Its elevation is in places nearly 200 ft. above the lake, and generally exceeds 160 ft. The sur- face on each side slopes away gradually, so that the line of the ridge is not everywhere distinctly defined. In other places it is plainly marked, having a base from 56 to 112 ft. across, and a width at the summit of about 33 ft. Sometimes it is divided into three or four par- allel ridges, which extend a few rods and then unite in one. Being composed of sand and gravel, it makes one of the finest natural roads in the world, and the principal highway along this side of the lake has been upon its sum- mit. There can' be little doubt that this ridge was an ancient shore line, and that within a recent geological period it has been formed by the waters of the lake. Besides its main feeder, the Niagara river, the principal streams which flow into Lake Ontario are the Gen- esee, Oswego, and Black rivers. The Os- wego is the outlet of almost all the lakes in the western part of New York. On the N. side of Lake Ontario a range of hills extend- ing parallel with the lake and a few miles back from it throws the drainage generally in other directions. The Trent river alone finds a passage through these hills, and flows with a number of smaller streams into the bay of Quinte, a long inlet extending about TO m. between the peninsula of Prince Edward near the foot of the lake and the mainland. The largest island in the lake, called Amherst isl- and, is at the mouth of this inlet ; it is 10 m. long and 6 broad. Many other smaller islands are met with at this lower extremity of the lake ; but excepting in this part the coast is very regular and unbroken. The principal towns in New York on the lake, or near the mouths of the streams which flow into it, are Lewiston on the Niagara river, Kochester on the Genesee, Oswego at the mouth of the Os- wego river, and Sackett's Harbor near the foot of the lake. In Canada, Kingston at the foot of the lake, Toronto 35 m. from its head, and Hamilton at the extreme head, are the largest towns on its shore. Its navigation is connect- ed with that of Lake Erie by the Welland ca- nal of Canada, 28 m. long. ONTOLOGY. See PHILOSOPHY. ONTONAGON, the extreme N. W. county of Michigan, bounded N. W. by Lake Superior, and S. W. by Wisconsin, from which it is sepa- rated in part by the Montreal river, and drained by the Ontonagon, Fire Steel, Iron, Presque Isle, and Black rivers; area, about 2,300 sq. m. ; pop. in 1870, 2,845. The surface is hilly, and an elevated range called the Porcupine mountains traverses the northern portion. It contains large quantities of copper and iron ore. In 1870 there were 10 copper mines worked, the products of which amounted to $256,802. The product in 1872 was 725 tons of ore. Capital, Ontonagon. ONYX, a variety of quartz, analogous to agate and other cryptocrystalline varieties, such as carnelian, jasper, chrysoprase, and bloodstone. It is composed of layers of different-colored carnelian, much like banded agate in structure, but the layers are in even or parallel planes, and the banding therefore straight ; on which account it is well adapted to the cutting of cameos, and was much used for that purpose by the ancients. The colors of the best are per- fectly well defined, and are either white and black, or white, brown, and black ; the finest specimens are brought from India, Many of the cryptocrystalline varieties of quartz, par- ticularly carnelian, contain variable small por- tions of opal, a hydrous quartz (see OPAL), which enhances their lustre and value. Sar- donyx has a structure like onyx, but is com- posed usually of alternate layers of white chal- cedony and carnelian (sard), although the ear- nelian may be associated with layers of white, brown, and black chalcedony. OOLITE (Gr. u6v, an egg, and Wog, a stone), limestone composed of rounded particles, like the roe or eggs of a fish. Each of the grains has usually a small fragment of sand as a nucleus, around which concentric layers of calcareous matter have accumulated. Ferru- ginous oolites are also found, as in the Clinton group in the United States, the investing ma- terial being in this case red oxide of iron. The name oolite is also applied to a group of strata of the Jurassic period, largely developed in England, in which limestone of this character occurs. The oolitic epoch is embraced be- tween the liassic below and the Wealden above, these three epochs forming the Jurassic period, the middle period of the reptilian age. The" oolitic formation contains limestones, part of which are oolitic in texture, and others arena- ceous and clayey, all being of marine origin except the Purbeck beds which rest upon the upper or Portland oolite. The following sub- divisions are recognized: 1. Lower or Bath oolite, containing, among other groups, fuller's earth and the great oolitic limestone, beneath which are the Stonesfield slates, near Oxford, noted for the remains of saurians, insects, and the earliest British mammals. There is also in the lower oolite in Sutherlandshire a bed of good coal 3| ft. thick, which has been worked for a long time. 2. Middle oolite, contain- ing calcareous grits with Oxford clay between. 3. Upper oolite, containing Kimmeridge clay, which furnishes material for Portland cement. 4. The Purbeck beds, consisting of lower, mid- dle, and upper Purbeck, which contain fresh- water marls, the "Portland dirt bed" being in the lower, and containing the second deposit of British mammals. OORT, Adam Tan, a Flemish painter, born in Antwerp in 1557, died there in 1641. He was instructed by his father, a painter of history,
