OF ORGANIC NATURE. 37 



what would be the practical effect of that movement ? 

 Why, that the sediment A and B which has been 

 already deposited, would eventually be brought nearer to 

 the shore-level, and again subjected to the wear and tear 

 of the sea ; and directly the sea begins to act upon it, 

 it would of course soon cut up and carry it away, to 

 a greater or less extent, to be re-deposited further out. 

 Well, as there is, in all probability, not one single 

 spot on the whole surface of the earth, which has not 

 been up and down in this way a great many times, it 

 follows that the thickness of the deposits formed at 

 any particular spot cannot be taken (even sup- 

 posing we had at first obtained correct data as to 

 the rate at which they took place), as affording reli- 

 able information as to the period of time occupied 

 in its deposit. So that you see it is absolutely ne- 

 cessary from these facts, seeing that our record 

 entirely consists of accumulations of mud, superim- 

 posed one on the other ; seeing in the next place that 

 any particular spots on which accumulations have 

 occurred, have been constantly moving up and down, 

 and sometimes out of the reach of a deposit, and at 

 other times its own deposit broken up and carried 

 away, it follows that our record must be in the highest 

 degree imperfect, and we have hardly a trace left of 

 thick deposits, or any definite knowledge of the area 

 that they occupied in a great many cases. And mark 

 this ! That supposing even that the whole surface of 

 the earth had been accessible to the geologist, — that man 

 had had access to every part of the earth, and had made 

 sections of the Avhole, and put them all together, — 

 even then his record must of necessity be imperfect. 



