CREATION BY EVOLUTION 



Jurassic rocks many of the coral reefs are isolated, occurring 

 at places where warm currents from the south raised the 

 temperature of the water. Most of these coral reefs have 

 disappeared, and thus, though the development of the Euro- 

 pean Montlivaltm may have been continuous, it appears dis- 

 continuous owing to the imperfection of the geological rec- 

 ord. In Europe it is therefore convenient to treat the separate 

 groups as species; but in India, where a large number of 

 corals were collected from one area of slightly undulating sea 

 floor, the variation is continuous. The groups of corals are 

 knots of individuals, or circuli. 



The opportunities for tracing progressive evolutionary 

 series of fossils in the field are not numerous; such series 

 can be found only where thick deposits have been laid down 

 continuously under the same geographical conditions, so that 

 for a long period forms were deposited one above another 

 and the intermediate forms were preserved in their right 

 order. The Chalk is one of the formations to which this 

 method can be applied. It is a soft, earthy limestone, in 

 places a thousand feet thick, and was laid down as an almost 

 continuous deposit of limy mud, so that the fossils are per- 

 fectly preserved and easily extracted; and owing to the many 

 uses of chalk large exposures are available in inland quarries 

 as well as in continuous sections in sea cliffs. Other groups 

 of Chalk fossils show the same continuous evolution as 

 Micraster. The process has been demonstrated in other for- 

 mations, as by Hyatt and others for the ammonites, by Car- 

 ruthers for a Carboniferous coral, by Schuchert and H. 

 Walker for the brachiopods. 



Opportunities for the study of contemporary variations are 

 more common, both with fossils and with living animals or 

 plants. Where organisms live in large numbers under simi- 

 lar conditions the attempt to divide species becomes practi- 



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