AGE OF THE STRATIFIED ROCKS 17 



rate from ancient to modern times, it would be incredible 

 that no clear proof of it should have been recorded in the 

 crust of the earth.' 



It may therefore be inferred that the rate of deposition 

 was no nearer the more rapid than the slower of the rates 

 recorded above, and, if so, the stratified rocks would have 

 been laid down in about 400 million years. 



There are other arguments favouring the uniformity 

 of conditions throughout the time during which the 

 stratified rocks were laid down, in addition to those 

 which are purely geological and depend upon the cha- 

 racter of the rocks themselves. Although more biological 

 than geological, these arguments are best considered 

 here. 



The geological agency to which attention is chiefly 

 directed by those who desire to hurry up the phenomena 

 of rock formation is that of the tides. But it seems 

 certain that the tides were not sufficiently higher in 

 Silurian times to prevent the deposition of certain beds 

 of great thickness under conditions as tranquil as any 

 of which we have evidence in the case of a formation 

 extending over a large area. From the character of the 

 organic remains it is known that these beds were laid 

 down in the sea, and there are the strongest grounds for 

 believing that they were accumulated along shores and 

 in fairly shallow water. The remains of extremely 

 delicate organisms are found in immense numbers, and 

 over a very large area. The recent discovery, in the 

 Silurian system of America, of trilobites, with their long 

 delicate antennae perfectly preserved, proves that in one 

 locality (Rome, New York State) the tranquillity of 

 deposition was quite as profound as in any locality yet 

 discovered on this side of the Atlantic. 



There are, then, among the older Palaeozoic rocks 

 a set of deposits than which we can imagine none better 

 calculated to test the force of the tides ; and we find 

 that they supply evidence for exceptional tranquillity of 

 conditions over a long period of time. 



There is other evidence of the permanence, through- 

 out the time during which the stratified rocks were 



