1819.] Greenough on the First Principles of Geology. 307 



Attention to this distinction will enable us likewise to appreciate 

 the value of some late notions that have emanated from the same 

 school, as that sandstone, traff-tuff, greywacke, &c. are chemical 

 deposits. 



Almost every kind of rock occurs both in a horizontal and a 

 vertical position. Now it has been very much agitated among 

 geologists, whether the vertical position of rocks was original, 

 or the consequence of some catastrophe subsequent to their 

 creation. Our author states the arguments on both sides with 

 much coolness and candour. The arguments to show that the 

 strata were originally horizontal are as follows : 



1. In some cases we observe the same strata on the one side 

 of a fault horizontal, while on the other side they are inclined. 

 Now in such cases it is infinitely probable that both were origin- 

 ally horizontal, and that this position was deranged on the one 

 side by the fault. This argument, therefore, is conclusive as far 

 as it goes. 



2. From the nature of the materials of which they are com- 

 posed, some strata, though at present vertical, must have been 

 originally horizontal. Thus it is impossible to suppose that the 

 vertical strata of loose sand that occur at Alum Bay were 

 originally deposited in that state. 



3. Inclined strata have sometimes the undulations on their 

 surface, which we meet with on a sandy beach. 



4. If the preceding arguments be admitted as conclusive, we 

 must go a step further ; for these beds are often so connected 

 with others below them that we cannot say where the series ends. 



These arguments seem sufficient to prove, that there are some 

 beds at present vertical or inclined that were originally horizon- 

 tal ; but I do not see how they give any countenance to the 

 notion that all vertical beds were originally horizontal. 



The arguments to show that the strata have remained unal- 

 tered are the following : 



1. It appears from veins that the particles of matter may 

 arrange themselves in beds highly inclined to the horizon. 



2. Inclined strata are often unaccompanied by marks of vio- 

 lence,and exhibitthe greatest regularity both in form and direction. 



3. Vertical or inclined strata are often mantle shaped. 



4. The rocks on the two sides of a mountain chain, as the 

 Alps, are often different. 



5. The irregularities in the strata seem to warrant that they 

 are in their original position. Thus at Malvern the inclination 

 of the sandstone diminishes as it recedes from the hill, and then 

 increases. To this succeed strata of limestone, the inclination 

 of which becomes more and more considerable. 



6. Secondary rocks are generally inclined at their junction 

 with primary. 



7. The secondary jocks are often unconformable to the 

 primary rocks on which they rest. 



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