408 Mr. H. G. Seeley on the. Laws which have determined 



is usually finer than shore-saud, and extends over a more limited 

 area. 



9. Sandj clay, and lime forming the sequence of rocks in 

 horizontal order {i. e. in space), it must also follow that there 

 will be a similar sequence in vertical order (i. e. in time). Thus, 

 therefore, it follows that if {g) a syenitic coast is denuded, and 

 the result is {s) sands, (c) clays, and (/) limestones, and the land 

 [g) is depressed so that high-water mark stands at x, then, the 



Depressed level of land {x). 



point from which the deposited materials are derived being car- 

 ried further inland {p), they will not be carried so far out to sea ; 

 hence a sand will be deposited near shore and continuous with 

 the old sand [s) ; a new clay will be deposited on top of the old 

 sand [s), and a new limestone on the old clay (c). But if the 

 land were to rise again, the place of origin for the deposited 

 matter would go further out to sea, the new deposits nearest 

 shore would be denuded, and sand be spread over the clay. If, 

 then, there is a sequence of rocks like the Secondary series, it 

 becomes extremely easy to determine all the changes in physical 

 geography that took place while they were accumulating, while 

 it is no less easy to predict what must be the representative of 

 a formation in a district where the mineral characters have 

 changed. 



10. Of course, organic causes and evaporation may accumu- 

 late limestones without their having any relation to sands and 

 clays, just as denudation of quartzites and sandstones may form 

 sands which are not succeeded by clays, and as the denudation 

 of volcanic rocks may form clays quite unconnected with sands 

 and limestones. 



11. The thickness of deposits in relation to time is to a large 

 extent dependent on climate. In tropical regions where evapo- 

 ration and the resulting rain are great, deposits of immense 

 extent are formed. In cold countries, though of small extent, 

 the deposits are liable, from the nature of the seasons, to a 

 similar alternation of characters with those of tropical countries. 



13. Every great fault changes the form and area of the sea- 

 bottom, and therefore modifies the sequence of deposits within 

 the disturbed area, producing unconformability if the fault is 

 formed rapidly. There is every reason to believe that faults 

 were as numerous in old geological times as in more recent pc- 



