973 



GEOLOGY. 



GEOLOGY. 



974 



into the hidden secrets of 

 the earth, and a similar fate 

 awaits their successors. 



To assume the truth of 

 either of these views is 

 altogether contrary to the 

 prudent spirit of modern 

 philosophy : no inspection 

 or analysis of the old 

 granitic masses ; no merely 

 analogical comparison of 

 them with the fluid com- 

 pounds of existing volca- 

 noes ; no a priori reasoning 

 will solve the question. 

 Yet it appears capable of 

 solution by a full and im- 

 partial consideration of the 

 stratified crust of the earth 

 itself, which ought to show 

 in the nature and condition 

 of the lower strata as com- 

 pared with the upper, and 

 in the nature and abund- 

 ance and mode of conser- 

 vation of organic remains, 

 evidence not only of the 

 circumstances under which 

 they were accumulated, 

 but indications of the na- 

 ture and extent of the 

 changes which have since 

 occurred to them. This 

 mode of inquiry we shall 

 endeavour to follow. 



This first diagram ia 

 intended to show how 

 very small is the supposed 

 depth of thn crust of the 

 earth, and of the most pro- 

 found parts of the ocean, 

 compared to the radius 

 of the globe. The thick- 

 ness of the crust of the 

 earth, here taken at 15 

 miles, is perhaps on a ge- 

 neral average not so much 

 as 5 miles. To this mere 

 film on the surface, of the 

 globe Inductive Geology is 

 confined ; though by help 

 of collateral science we 

 have learned many truths 

 as to the constitution of 

 the hidden interior masses. 



The difference of the 

 diameters of the earth is 

 nearly 26 miles. If the 

 axis of the globe were 

 displaced 90 degrees, the 

 level of the sea would rise 

 at the old poles and sink 

 at the new poles about 

 half that quantity, or 13} 

 miles; and at other points 

 intermediate quantities, 

 according to their rela- 

 tions to the great circle 

 passing through the new 

 and old poles of rotation. 

 At the poles of this great 

 circle there would be no 

 alteration of level. 



By imagining the depth 

 of 1000 miles, in the first 

 diagram on the following 

 page, to be repeated three 

 times, and the three radii 

 to be at the same time pro- 

 longed till they meet at a 

 point, which would repre- 

 sent the centre of the earth, 

 the reader will easily form a 

 notion of what ia intended. 



The arc includes 20 degrees from the Adriatic to the Atlantic, 

 passing over the Apennines, the Alps, the English Channel, the Welsh 

 Mountains, and the Irish Sea, the depth of the narrow seas being less 

 than the breadth of the fine lines. 



The general section (fig. 3), combined with the complete table of 

 British strata which follows (extracted from Phillips's ' Guide to Geo- 

 logy ') will serve for reference to the reader who may be unacquainted 

 with the arrangement of the stratified rocks in the crust of the earth. 



