444 ON THE GEOLOGICAL RELATIONS 



because it explains such cases as that of the Paris basin, 

 and many more: it will be a future intermixture or 

 alternation of marine and terrestrial remains, in shale 

 and sandstone and limestone; a study for the geologists 

 of other Earths. 



On analogous grounds, mayjiot only many of the 

 cases of the tertiary deposits, but those of the Lias 

 also be explained. Wherever this series presents such 

 intermixtures, that point at least was an aestuary: the 

 solution is simple, and it offers a perfect analogy to 

 the aestuary of the Thames, or any other river, at 

 present. The same mixtures from transportation are 

 occurring there; and in future ages, or worlds, it may 

 be a lias series, thus far. The alluvial antient aestua- 

 ries, just mentioned, are parallel cases under another 

 form. And in actual aestuaries, as in more antient 

 ones, marine and terrestrial remains, antient and 

 modern ones, may often be confounded, since the proper 

 marine bottom must be frequently mixed with the 

 terrestrial deposits of the rivers, and in every manner. 

 Cases of actual distant transportation, such as that of 

 West Indian fruits to our own shores, seem too limited 

 in quantity and possible effect, to demand any re- 

 ference to antient deposits. 



To guide the judgments of geologists on this sub- 

 ject, I must yet remark, that in such cases, errors 

 may arise, first from mistaking the origin of the fos- 

 sils themselves, and next from mistaking the nature 

 of the strata; as it would be easy to point out re- 

 corded cases where both have been combined. And 

 thus have such mistakes arisen, from determining 

 the origin of the stratum through the presumed one 

 of the fossil, or that of this last, from misapprehending 

 the nature of the other. 



In. the chapter on the tertiary strata, I have already 



