134 



THE GEOLOGIST. 



triumphantly produced by the anti-transmutationists ; if, on 

 the contrary, it has changed in ever so slight a degree from an 

 extinct form it is called a new species. 



4. Suppose a large area covered with sea, and Lingula, &c, spread 



over it. Now suppose a part of this area to be gradually 

 elevated, the Lingulae and other animals living on it would 

 undergo variation to meet the change of conditions ; but those 

 on the stationary area would remain constant. Next suppose 

 the elevated part to sink again : the new forms on it must 

 either die out or change, and the Lingulae would again spread 

 over the whole area ; and being better adapted to those con- 

 ditions, from long residence in them, would kill off, perhaps, 

 some of the new forms. Again, another part of the area 

 might be raised ; and so on. The chances are that some of 

 the Lingulae would always be on a stationary portion, and thus 

 hand down their offspring with little variation, for any length 

 of time. It is a fact which strongly corroborates this, that 

 nearly all the genera which have a long range in time are 

 inhabitants of the deep sea, and therefore have also a large 

 range in space. 



5. It is not supposed that the armadillo is descended from the 



glyptodon ; on the contrary the latter seems to have become 

 extinct, and to have left no progeny, while some other form 

 may have been the progenitor of the former. 



6. " On the contrary domestic breeds show all degrees of variation, 



as the pigeon, dog, &c, on one side, and the cat and goose on 

 the other. Perhaps there is not much difference of variability 

 in animals, constancy can generally be accounted for ; pigeons 

 can be mated for life, and are kept in large quantities, and 

 therefore vary much ; cats ramble at night and cannot be 

 watched, and are kept in small quantities ; donkeys and pea- 

 cocks are also kept in smart quantities, and the breeding of 

 donkeys is not much cared for ; geese are only valued for 

 1 wo purposes, food and feathers, and no pleasure seems to have 

 been felt for different breeds." 



Let us now see what reasons there are for supposing that variation 

 is nl jn-rsrnl unlimited; or, in other words, that all animals have de- 

 scended from a common prototjnpe. By admitting it to be true we 

 can easily understand — 



1. Why species have come into the world slowly and successively 



2, Why '• fche Families of each division (of moluscs) which are least 



unlike (OrthoceraMdce and Belemnitidce) were respectively the 

 first developed.* 



■ k Why species have not necessarily changed together, or at the 

 same rate, or in fche same degree; yet in the long run all have 

 undergone modification to some extent. 



* Woodward's "Recent and Fossil Shells," p. 417. 



