AMERICAN GEOLOGY— THE EOZOON QUESTION. 



637 



ous part. This in turn became again broken, leaving in some places 

 uninjured portions of the general form. 



The main difference between this foraminiferal reef and more recent 

 coral reefs, he thought to be, that, while with the latter there arc 

 usually associated many shells and other organic remains, in the more 

 ancient one the only remains yet found were those of the animal which 

 built the reef. 



Dawson attacked the problem from the zoologist's standpoint. To 

 properly understand his position and also that of those who combated 

 his arguments, it must be remembered that the science of micro- 

 petrography was then in its infancy; in fact the possibilities of meta- 

 somatosis or alteration by indefinite substitution and replacement were 

 only beginning to be realized by even the most advanced of mineralo- 

 gists and geologists. Hence it was possible for two men, attacking 

 the same problem from opposite 

 standpoints — the one as a chemist 

 and physicist and the other as a 

 zoologist — to arrive at conclu- 

 sions diametrically opposed to 

 each other. 



The specimens examined, as 

 already indicated, were masses 

 often several inches in diameter, 

 presenting to the naked eye al- 

 ternate lamina? of serpentine, or 

 pyroxene, and carbonate of lime, 

 their general aspect reminding 

 one, as already noted, of the Silu- 

 rian Hydroids of the genus Stro- 

 matopora (see tig. 124:). Under 

 the microscope Dawson found 

 the lamina 1 of serpentine and p} T roxene to present no organic structure, 

 the pyroxene being highly ciystalline. The laminae of carbonate of 

 lime, on the other hand, he thought retained distinct traces of struc- 

 ture which could be considered only as organic, constituting parallel 

 or concentric partitions of variable thickness inclosing flattened spaces 

 or chambers, frequently crossed by transverse plates or septa. The 

 lamina' themselves were frequently excavated on their sides into 

 rounded pits, and in some places traversed 1>3 T canals and penetrated 

 by numerous minute tubuli, a structure which can be best understood 

 by a reference to fig. 126. 



According to the conclusions of Dawson, the calcareous portion rep- 

 resented the portion of the original shell, the serpentinous matter, on 

 the other hand, being material infiltrated into the cavities which had 

 been occupied by sarcode during the life of the animal. He referred 



Fig. 126.— Magnified group of canals in supple- 

 mental skeleton of Eozoon. Taken from the 

 specimen in -which they were first recognized 

 (Life's Dawn on Earth). (After J. W. Dawson.) 



