Masterpieces of Science 



of the earth's crust or desolation of the surface 

 since times the most remote. The non-occur- 

 rence of such a general convulsion is proved by 

 the perfect horizontality now retained by some 

 of the most ancient fossiliferous [fossil bearing] 

 strata throughout wide areas. 



That the subterranean forces have visited 

 different parts of the globe at successive periods 

 is inferred chiefly from the unconformability of 

 strata belonging to groups of different ages. 

 Thus, for example, on the borders of Wales and 

 Shropshire, we find the slaty beds of the ancient 

 Silurian system inclined and vertical, while the 

 beds of the overlying carboniferous shale and 

 sandstone are horizontal. All are agreed that 

 in such a case the older set of strata had suffered 

 great disturbance before the deposition of the 

 newer or carboniferous beds, 'and that these last 

 have never since been violently fractured, nor 

 have ever been bent into folds, whether by sud- 

 den or continuous lateral pressure. On the other 

 hand, the more ancient or Silurian group suffered 

 only a local derangement, and neither in Wales 

 nor elsewhere are all the rocks of that age found 

 to be curved or vertical. 



In various parts of -Europe, for example, and 

 particularly near Lake Wener in the south of 

 Sweden, and in many parts of Russia, the Silurian 

 strata maintain the most perfect horizontality; 

 and a similar observation may be made respect- 

 ing limestones and shales of like antiquity in the 

 great lake district of Canada and the United 

 120 



