74 



GEOLOGICAL BIOLOGY. 



be bodily shifted seaward by elevation, and landward by de- 

 pression of the continental border. 



Order of Deposits with a Sinking Land. — Other conditions 

 remaining the same, for instance, on a shore with land to 

 the westward and ocean to the eastward, a gradual continu- 

 ous depression of the land would result as follows: The shore- 

 line would gradually retreat westward ; at each spot the water 

 would gradually become deeper and further off shore ; and, 

 considering only this one law of sedimentation, the deposits 

 forming at each spot would gradually become finer and finer 

 with the progress of time ; so that finally it would happen 

 that the deposit forming directly over the place where the 

 shore-line was at the outset would be the very fine silt peculiar 

 to deep water far out from shore, the same which at the 

 beginning of the period was being deposited only at a distance 

 off shore. 



To compare the sections taken at three localities we would 

 get the following results, seen in Fig. 3 : 



West. 



East. 



Pig. 3. Three different sets of deposits formed during the same periods of time at three points, 



I, "2, and 3, separate from each other, with a sinking of the land as the sediments are 

 accumulated. 



In which the section at i would exhibit a series of deposits, one 

 overlying the other {a b c), presenting the same differences of 

 sedimentation that would be exhibited on comparing the first 

 deposits in the several sections {a a' a"). It is likely, too, 

 that the general character of the fossils would correspond, but 

 as a matter of age the deposits of like character in the three 

 sections {a" b' c) would represent consecutive periods, instead 

 of the same period of time. 



Order of Deposits with Elevation of the Land. — If we sup- 

 pose a gradual elevation to take place, instead of depression, 

 then the shore-line would advance gradually seaward, — east- 

 ward in the supposed case, — and the first locality (i) would 



