SjovAitr 80, 188B.I
��stnictural clianges Induced by iiieclmiiiciil movements ia ancient crysLilline rocks have nothing in common with that myaterious. |iroces9 which has been supposed by the meta- morpbic school to generate similar crystalline rocks fVom non-crystalline sediments. As re- gards [he chtiDges wrought by the same agency' in detrilal masses, it may be re|)eated Ihut "the resemblances between primiiive crystal- line rocks and what we know lo he detrilal rocks, compressed, recemeuted, and ofteti exhibiUng interstitial minerals of secondary origin, are too slight and superficial to deceive the critical student, and disappear under mi- croscopical investigation."
The doctrine of a regional and progressive metamorphism as the origin of the crysLnlliDe rocks, which was very widely received a gener- alion since, both in Europe and America, hat^ within the lost fourteen years become greatly discredited. In the Alps, where it was first seriously applied, as well as in Great Britain. it is now generally abandoned. Callaway wrote not loug since, that " every case of supposed iiictamorphic Cambrian and Silurian has been invalidated by recent researches;" and Bonney. now president of the Geological society of London, declared, in 1883, that the hitherto accrertiied •* instances of metamor- phism in Wales, and especially in Anglesea. iu Cornwall, in Ibices Lersh ire, and in Worces- tershire, have utterly broken down on careful study," as had already been the case in the Alps, and. it may be added, in North America. The oftlcial geologists in Great Britain, repre- senting the irndilions of the old school, have, however, hitherto held to the Scottish High- lands as their last stronghold, which they are now forced to abandon- — u substantial victory for rational geology.
T. Sterkv IltNT.
Ma mnal. J«i. 10.
^^^febR U. S. hydrographic office having sent ^^Hulhe N'ew-Orleans exposition, as part of its ^^Hnbit, a model of the Caribbean Sea, it will ^^8 interesting nt this time to discuss the deep- sea soundings taken by officers of the navy in the coast -survey steamer Ulake, and in the Hsh- commission st«amer Albatross, from IST^t to 1884, by means of which this moilel was con- atnicteti.
Particular attention was called to this great
I in in the coast-suney reports for 1H80 and I, and also in a paper read by the writer
��THE BASIN OF THE CARIBBEAN.
��before the American Geographical Society in the winter of 1882.
It was not |)Ossible, however, to give the contour of the lied of this sea until the com- pleiiun of the work of the Albatross last win- ter. The data then obtained pennilled the construction of the occompuiiying chart, which is a faithful representation of the model before mentioned, and by means of which it will lie easy to draw attention to some of '\ts most im- [lortant features.
During the cruise of the Challenger, it was demonstrated that in a submarine lake the tcra- iwrature is constant to tbe greatest depth, and the same as that of the ocean at the depth of the rim of the lake at its lowest or dec|>est point.
The investigations of the temperature of the Gulf of Mexico by Commander Sigsliee, iVoni 1874 to 1878, had shown that below a depth of 800 fathoms the temperature is couslaut at 39i°, which is the normal temperature of the ocean at that deptli in the region of the Kquatorial Current. It was evident, therefore, that the Caribbean Sea. from which the Gulf of Mexico receives its waters, must be enclosed by a rim which at its deejiest part was 800 fathoms below the surface.
The purpose of the investigations of the lilake. during the time that 1 had the honor tu command, was to verify the deduction thus made, and to determine the |)osition and height of this rim, which limits the low temperature of the waters of the Gnlf of Mexico- All the passages between the island.'^ fi-om Trinidad to Cuba were carefully sounded, and the existence and [wsilion of the rim definitely established. At the same lime temperatures were taken both outside and inside the basin, and at the points of minimum depth. With one L-xcepiion. however, the only place where the rim was sufficiently low to admit water of the required tem|>erature (3!)}°) was in the windward passage. In all other places the depths on the r\ia were much less than ■■*0{> fathoms.
The exception noted was a nairow gully of 1,100 fathoms, with a bottom lcm|jeratnre of 38°, leading into a basin of 2,400 fathoms be- tween Santa Cruz and St. Thomas ; this great depth also having a bottom temperature of 38°. .■\9 the temperature at 1 .500 fathoms Just south of Mona Passive was 3'JJ°, there could be no doubt of the existence of a rim from h&aia, Cruz to Puerto Kico. The Albatross, there- fore, was directed to examine this locality, and, us was expected, found the ridge with 900 fathoms on it at the greatest deplh. and a leasl
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