AND STRATIFICATION. 77 



darkness of night or the haziness of the weather con- 

 ceals the land from his view. 



It has heen observed that, in many places, certain 

 strata of different natures are usually associated in 

 groups, as they may be termed, or that one rock of a 

 remarkable character is interstratified with a minor 

 quantity of others, for a certain depth before it finally 

 ceases to give way to another equally conspicuous. 

 Thus, for example, gneiss and hornblende schist are 

 frequently found united, and the latter in small pro- 

 portion to the former; and thus the red marl sand- 

 stone of England, contains beds of clay, shale, and 

 limestone. These minor strata have been called sub- 

 ordinate; a term, the nature and abuse of which is ex- 

 amined in another place; and to these associations 

 the very awkward name formation has been applied. 

 It has been supposed that the invention 6f this term 

 has been of great use to Geology, by generalizing 

 certain observations; and it is also imagined that 

 many such format ions are really definite and constant. 

 That cannot be denied; nor will the utility of the ex- 

 pedient, in some cases, be questioned. But it is 

 obvious that this scheme savours too much of hypo- 

 thesis, and that it may become a fertile source of that 

 gratuitous and unfounded generalization against 

 which the young geologist has already been cautioned. 



Of the Nature and Causes of Stratification. 



That the strata could not have been deposited from 

 solution in water, is sufficiently shown elsewhere, and 

 it is therefore unnecessary to dwell on it here (Chap, xii.) 

 It is to mechanical deposition, in a more or less gra- 

 dual manner, and from suspension in water, that we 

 must attribute their origin, as is more fully shown in 



