590 Geological Society, \ 



it by a system of parallel but vertical fissures ; and that subsequent 

 elevations and subsidences of the disjointed masses would produce 

 anticlinal and synclinal lines. In the Cordillera, the strata in the 

 central parts, are inclined at an angle commonly exceeding 45°, and 

 are very often absolutely vertical, the axis being composed of granitic 

 masses, which, from the number of dikes branching from them, must 

 have been fluid when propelled against the lower beds. How then, 

 he asked, could the strata have been placed in a highly inclined and 

 often vertical position, by the action of the fluid rock beneath, with- 

 out the very bowels of the earth gushing out ? If, on the other hand, 

 it be supposed that mountain-chains were formed by a succession of 

 shocks similar to those which elevated Concepcion, and after long 

 intervals, time would be allowed for the injected rock to become 

 solid, as well as the upper part of the great central mass. Thus, by 

 a succession of movements, the strata might be placed in any posi- 

 tion ; and the crystalline nucleus gradually thickening, would pre- 

 vent the surface of the surrounding country being inundated with 

 molten matter. 



In crossing the Andes, Mr. Darwin was surprised at finding, not 

 one great anticlinal line, but eight, or more ; and that the rocks com- 

 posing the axes were seldom visible, except in denuded patches in the 

 vallies. This circumstance, he conceives, must be due to the thickness 

 of the upheaved strata being equal, or nearly so, to the average 

 distance of the anticlinal from the synclinal lines. For in that case, 

 the masses of strata, when placed vertically, would occupy, or rest 

 on, as great an horizontal extent, as they did before they were dis- 

 turbed. 



In the central ridges of the Cordillera, there are masses of com- 

 pact, unstratified rocks, half again as lofty as ^tna ; and these, he 

 believes, for the reasons before stated, were formed by the gradual 

 cooling of the subjacent fluid mass ; afterwards slowly elevated 

 to the present position, by the injection of molten matter at nearly 

 as slow a rate, as we must suppose the innumerable layers of vol- 

 canic products, of which the Sicilian mountain is formed, have been 

 ejected. 



In conclusion, Mr. Darwin repeated the argument, that moun- 

 tain-chains and volcanos are due to the same cause, and may be 

 considered as mere subsidiary phsenomena, attendant on continental 

 elevations ; — that continental elevations, and the action of volcanos, 

 are phsenomena now in progress, caused by some slow but great 

 change in the interior of the earth ; and, therefore, that it might be 

 anticipated, that the formation of mountain-chains is likewise in pro- 

 gress ; and at a rate which may be judged of, by either actions, but 

 most clearly by the growth of volcanos. 



March 21st. — A paper was first read, on the Dislocation of the 

 Tail, at a certain point, observable in the skeletons of many Ich- 

 thyosauri, by Richard Owen, Esq., F.G.S., Hunterian Professor to 

 the Royal College of Surgeons, London. 



Mr. Owen commences his observations by referring to the skele- 

 ton of the existing cetacea, and pointing out how slight is the indi- 



