DOCTRINE OF GEOLOGICAL CONTINUITY. 27*3 



character, so that, on reaching their new destination, some of them 

 might be hardly recognisable as the same species. This would 

 be further aided and increased by their having to compete with 

 strange competitors. In any case, their remains would be preserved 

 in the sedimentary rocks of the new area. 



When, millions of years afterwards, we come to examine the earth's 

 crust, and we find in two widely remote areas two series of strata 

 containing certain identical and characteristic species, we naturally 

 say: *' These rocks are contemporaneous." It is clear, however, that 

 if they had been formed in the manner we have been supposing, we 

 should be wrong in this conclusion. The rocks in question would 

 belong to the same geological period, and they would in part contain 

 the same fossils ; but they would belong to different stages of the 

 same period, and they would not, therefore, be strictly " contempo- 

 raneous." To use a term applied by Professor Huxley to rocks 

 believed to hold this relation to one another, they would be " homo- 

 taxeous " deposits. 



"What I have just said about the Carboniferous rocks would 

 apply with equal justice to all the great formations, and to 

 many of the smaller rock-groups all over the world. The Silurian 

 rocks of Europe, North America, South America, Australia, &c., 

 contain very similar fossils, and are undoubtedly " homotaxeous." 

 Nothing, however, that we can see at the present day, would warrant 

 us in believing that they are " contemporaneous," in the sti-ict sense 

 of this term. This is more especially the case with some of the 

 minor subdivisions of the Silurian and Cambrian rocks, which have 

 been shown to contain exactly the same fossils in parts of the world 

 widely removed from one another. (For example, some of the 

 peculiar Graptolites of the Quebec or Skiddaw series, are common to 

 Canada, the north of England, and Australia.) The very closeness 

 of the resemblance of the fossils, or the very ideritity of the species, 

 is just what proves that the beds in question, from their geogra- 

 phical position, can not have been deposited exactly at the same time, 

 though they doubtless belong to the same period, and may even be 

 said to be related to one another by lineal descent. Similar remarks 

 might be made about the Devonian, Permian, Triassic, Jurassic, Creta- 

 ceous, and other formations ; but it is unnecessary to multiply 

 examples. 



