GNEISS, MICA-SCHIST, &c. 25 



15. Granite, which seems to form the first basis, the foundation 

 stone of the great -^oiogical edifice, remains uncovered at various 

 points on the surface of the earth, while in other places it is 

 covered by more or less numerous beds of more recent formations. 

 But all the granitic rocks now scattered over the surface of the 

 globe do not date from an antiquity so remote ; for, in different 

 recent epochs, mineral materials in a state of fusion have escaped 

 from the bosom of the earth, which spread over formations then 

 existing, and, on cooling, constituted immense masses of granite 

 s milar to that first formed. 



16. This rock is met with in different places in all parts of the 

 world, and is employed in the construction of edifices of various 

 description. 



17. The beds which are deposited on the first massive crust of 

 the globe are crystalline in structure, and this character is more 

 decided the more ancient they are ; they seem to have been ex- 

 posed to the action of a great heat, without possessing the charac- 

 ters of rocks of igneous origin. They consist principally of gneiss, 

 mica-schist, and argillaceous schist. 



18. Gneiss is a rock very analogous to granite as respects its 

 elementary constituents, but its structure is foliated and presents a 

 stratified arrangement ; it appears to have been formed under wa- 

 ter, and seems to be the most ancient of the sedimentary forma- 

 tions, because in certain places on the surface of the globe we find 

 it covered by all the other formations. We often see it naked ; it 

 forms vast systems of rocks in which it is often alternated with 

 mica-schist and other ancient rocks. It is used in building and 

 flagging. 



19. Mica-schist is a lamellar rock composed of quartz ordinarily 

 grayish, and a great quantity of brilliant lamellae of mica arranged 

 in extended leaves or scales ; it commonly accompanies granite and 

 gneiss. 



20. Jlrgil/aceous schist is in appearance an earthy rock, which 

 is easily divided into large laminae more or less thin, and was evi- 

 dently formed under water by the deposit of sediment. [Schist, 

 from the Greek schist os, slaty, easily split.] 



We also find in these primitive strata compact limestone of great 

 hardness, and other rocks which more or less resemble the pre- 

 ceding. 



21. These different rocks, the origin of which dates from the 



15. Is granite everywhere hid beneath the surface of the earth? Is ail 

 granite supposed to be of the same age ? 



16. Where is granite found? To what uses is it applied? 



17. What kind of rocks are found overlying the granite? 



18. What is gneiss? How does it seem to have been formed' 



19. What are the characters of mica-schist? 

 20 What is argilla'ceous schist ? 



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