PALiEON'TOLOGICAL COLLFXTION'S 345 



formed the primordial nucleus of the globe, will admit that 

 these latter rocks have been stript of their covering to an 

 enormous extent. For it is scarcely possible that such rocks 

 could have been solidified and crystallized whilst uncovered; 

 but if the metamorphic action occurred at profound depths of 

 the ocean, the former protecting mantle of rock may not have 

 been ver>- thick. Admitting then that gneiss, mica-schist, 

 granite, diorite, &c., were once necessarily covered up, how 

 can we account for the naked and extensive areas of such 

 rocks in many parts of the world, except on the belief that 

 they have subsequently been completely denuded of all over- 

 lying strata? That such extensive areas do exist cannot be 

 doubted; the granitic region of Parime is described by Hum- 

 boldt as being at least nineteen times as large as Switzerland. 

 South of the Amazon, Boue colours an area composed of 

 rocks of this nature as equal to that of Spain, France, Italy, 

 part of Germany, and the British Islands, all conjoined. This 

 region has not been carefully explored, but from the concur- 

 rent testimony of travellers, the granitic area is very large; 

 thus, Von Eschwege gives a detailed section of these rocks, 

 stretching from Rio de Janeiro for 260 geographical miles 

 inland in a straight line; and I travelled for 150 miles in 

 another direction, and saw nothing but granitic rocks. Nu- 

 merous specimens, collected along the whole coast from near 

 Rio Janeiro to the mouth of the Plata, a distance of iioo geo- 

 graphical miles, were examined by me, and they all belonged 

 to this class. Inland, along the whole northern bank of the 

 Plata I saw, besides modern tertiary beds, only one small 

 patch of slightly metamorphosed rock, which alone could 

 have formed a part of the original capping of the granitic 

 series. Turning to a well-known region, namely, to the 

 United States and Canada, as shown in Professor H. D. 

 Rogers's beautiful map, I have estimated the areas by cutting 

 out and weighing the paper, and I find that the metamorphic 

 (excluding "the semi-metamorphic") and granitic rocks ex- 

 ceed, in the proportion of 19 to 12-5, the whole of the newer 

 Palaeozoic formations. In many regions the metamorphic and 

 granitic rocks would be found much more widely extended 

 than they appear to be, if all the sedimentary beds were re- 

 moved which rest unconformably on them, and which could 



