OF ORGANIC NATURE. 37 



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 supposing 

 we had at first obtained correct data as to the rate at 

 which they took place), as affording reliable informa- 

 tion as to the period of time occupied in its deposit. 

 So that you see it is absolutely necessary from these 

 facts, seeing that our record entirely consists of accumu- 

 lations of mud, superimposed 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 roach 

 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 groat many <■■ 

 And mark this! That supposing even that the whole 

 surface of the earth had been accessible to the geolo- 

 gist, — that man had had access to every part of the 

 earth, and had made sections of the whole, and put 

 them all together, — even then his record must of neces- 

 sity be imperfect. 



But to how much has man really access \ If you 

 will look at this Map you will see that it represents 

 the proportion of the sea to the earth : this coloured 

 part indicates all the dry land, and this other portion 

 is the water. You will notice at once that the water 

 covers three-fifths of the whole surface of the globe, 

 and has covered it in the same maimer ever since man 

 has kept any record of his own observations, to say 



