408 



MINERALOGY. 



tain. 



PlATt 



cccxcv. 

 Fig. 9. 



Fig. 



Geognosy. 5, y/je Relation of the Outgoings of the Strata to the 



*"" ""V""' terior of the Mountain. 



The rela- 

 tion of the y/ e [ l&ve to consider first, the relation of the outgo- 

 inns of strata to mountain-masses of considerable ex- 



cl tnc stra- & .. . 



ta to the tent ; and, secondly, to mountain caps. 



exterior of In mountain-masses, the strata either cover each 



the moun- other completely, or the outgoings are open and ex- 

 posed. When the outgoings are exposed, the newer 

 strata have a rising or sinking level, Fig. 9. 



There are three different kinds of mountain-caps: 

 In the Jirst, the cap rests on a fundamental rock, the 

 seams of the strata are parallel with the plane on 

 which the strata rest, and these are unconformable 

 lo. a. and overlying, Fig. 10. a. The second kind of cap 

 is formed by a rock rising through the surrounding 



Fig. 11. &. strata, Fig. 11.6.: and the third kind of cap is form- 

 ed by portions of harder beds remaining after t the su- 

 perincumbent and adjacent and softer strata have been 



Fig. 12. c. carried away, Fig. 12. c. 



In the Jirst, the rock is unconformable and overly- 

 ing. The secondary-trap and porphyry formations 

 afford numerous examples of this kind of mountain-cap. 

 In the second, the newer strata are mantle- shaped. 

 Granite often occurs in caps of this kind. 



In the third, all the strata are conformable, so that 

 the subjacent and superincumbent strata have the 

 same direction with the bed which forms the cap. 

 Primitive greenstone in clay-slate, sometimes forms 

 caps of this kind. 



CHAP. IV. 



ON THE FORMATION OF ROCKS, AND ON FORMATIONS. 



On the for- Having now described the different kinds of struc- 

 motion of ture which occur in the crust of the earth, we shall 

 rocks. nex t treat of the formation of mountain rocks, and of 

 the revolutions which the earth is alleged to have expe- 

 rienced during its formation But those revolutions are 

 of a different nature from the effects now produced on 

 the surface of the earth ; and therefore the specula- 

 tions in regard to them are to be considered more in- 

 teresting on account of the facts they bring to light, 

 than from any intrinsic merit they themselves possess. 

 The most ingenious of these speculations respect- 

 ing the formation of the earth hitherto proposed, is 

 that of Werner; and the following statement will, 

 we think, convey to our readers a distinct account of 

 it. 



The spheroidal figure of the earth, its crystalline 

 and stratified structures, and its numerous petrifac- 

 tions, are proofs of its original fluidity. The fluidity, 

 according to Werner, was aqueous ; and he conjec- 

 tures that the various rocks were originally suspended 

 or dissolved in water, and gradually deposited from it. 

 In chapter second, when mentioning the effects of 

 water on the surface of the globe, we described several 

 mechanical and chemical depositions which are daily 

 taking place, as it were, under our eye ; and as these 

 present the same kind of structure that occurs in moun- 

 tain rocks, Werner infers these also to have been formed 

 by the same agent. As the highest mountains are com- 

 posed of rocks, possessing a structure resembling those 

 fossils which have been formed by water, we natu- 

 rally conclude, that the ocean must have formerly 



stood very high over these mountains. Further, as Geognoip. 

 the most elevated mountains are composed of rocks, > "^V"^ 

 such as granite, gneiss, mica-slate, clay-slate, and 

 others, which extend around the whole globe, and 

 have been formed during the same period of time, it 

 follows, that the ocean must have formerly covered ike 

 whole earth at t/ie same time.. The former great height, 

 and the present low level, of the waters of the globe, 

 is so remarkable a phenomenon, that it gave rise to 

 many very opposite hypotheses, as soon as it attracted 

 the attention of observers. We shall notice a few of 

 these speculations. 



It has been supposed, that the water has suffered a 

 translocation, by a complete alteration of the terres- 

 trial poles and equator. This hypothesis, however, is 

 unsupported by fact, as no traces are to be found of 

 so vast a change. The difference between the equato- 

 rial and polar diameters, the accumulation of high 

 land around the equator, are proofs that the present 

 poles and equator are the original ones. Even allow- 

 ing that such a change had taken place, it is evident 

 that the greatest possible alteration of the earth's axis 

 could cause no uncovering of it, as the water stood 

 high over the whole globe. 



Another opinion was proposed by De Luc, La Me- 

 therie, and others ; namely, that the water had retired 

 into immense caverns, situated towards the centre of 

 the earth. From the description already given, of the 

 internal structure of the earth, it is evident that the 

 existence of such caverns is imaginary and totally irre- 

 concileable with the notion of precipitation from a 

 state of solution. Allowing for a moment the possi- 

 bility of their existence, is it not evident, not only 

 that the water would have rushed into them with such 

 violence as to leave the most marked traces of its effects 

 on the surface of the earth, but that the places where 

 the water entered would still be discoverable ? 



The most probable explanation is that of the gradual 

 diminution of the water from the surface of the earth. 

 It was first obscurely hinted at by Herodotus, Strabo, 

 and other ancient writers. Maillet, French consul at 

 Alexandria, in ft wprk entitled Tellianied, published in 

 1740, was the first in modern times who directed the 

 attention of philosophers to the theory of the diminu- 

 tion of the waters of the globe. This opinion was ea- 

 gerly adopted, and keenly supported by Linnaeus, Cel* 

 sius, and other Swedish naturalists. They collected 

 many facts, to show that the waters of the Baltic are 

 diminishing ; and the scholars of Linnaeus observed 

 many similar appearances in other countries. Of these 

 many interesting instances are detailed in the writings 

 of Pallas, Gmelin, Ferber, Niebuhr, Vancouver, Per- 

 ron, and others. Even although all these proofs were 

 wanting, it is evident that if the water remained unal- 

 tered in quantity, it would rise and overflow its bound- 

 ary, owing to the great quantity of earthy matter which 

 is daily carried into it by rivers and streams. This 

 opinion, as supported by Linnaeus and several others, 

 met with considerable opposition. Many facts were 

 brought forward, to show, that while the land is left 

 by the sea in one place, it is invaded in an equal pro- 

 portion in another ; and consequently that there is no 

 diminution of the water. The invasion of the land by 

 the sea, is, however, a comparatively rare occurrence; 

 and besides, these partial elevations of the water de- 

 pend on particular circumstances, which can in gene- 

 ral be pointed out. Thus, the change in the direction 

 of currents, produced by the accumulation of water by 



