THE CRUST OF THE EARTH. 



being the most prompt to sink. Next would come layers of less- 

 ponderous matter, and then another lighter still, and thus layer 

 upon layer would be deposited until the whole of the suspended 

 matter would have subsided. 



If from any cause after this subsidence the water retired, the 

 ground forming its bottom would be left bare, and the dry land 

 would, if it were excavated, be found to consist of the succession 

 of strata here described. 



Now if the actual layers composing the successive strata, which 

 are superincumbent on the igneous rocks, did really in their 

 origin proceed from such a cause, it might be expected that they 

 would succeed each other in the order here indicated, those most 

 apt to subside holding the lower position, and such accordingly is- 

 found to be the case. 



30. In accordance with these results of observation on the 

 strata forming the crust of the earth, and with concurrent 

 evidence deduced from other appearances, it has been inferred,, 

 with a degree of probability amounting to moral certainty, that 

 the stratification has resulted from such a series of physical, 

 causes as those above described. Each stratum consisting of a 

 series of parallel layers is assumed to have been a sedimentary 

 deposit precipitated from water, by which the surface of the solid 

 part of the globe has been at former epochs covered, and that 

 these waters having become quiescent before retiring, the matter 

 suspended in them was deposited in layers having more or less 

 regularity, their surfaces being parallel and level, or nearly so. 



31. Among the many collateral circumstances which corro- 

 borate these conclusions may be mentioned two. 



First, the frequent occurrence in the bounding surface of the- 

 layers of the form of the ripple of water, as it is observed in the 

 sands of the sea shore after the fall of the tide has laid them bare.. 



An example of such traces left upon the beds of carboniferous 

 limestone and Portland-stone, in the neighbourhood of Boulogne,, 

 is shown in fig. 2. 



Fig. 2. 



Secondly, by the remains of various aquatic animals and 

 plants, which are often preserved in their natural position, in 

 42 



