174 PERIDOTITE. 



that zoologists and palJBontologists, however skilled they may be in the 

 study of organized remains, tend to extend that kingdom in which they 

 have most experience over every form of the mineral world simulating 

 organic forms. So, too, it is not to be denied, on the other hand, that 

 mineralogists and lithologists are likewise prone to unduly extend their 

 kingdom. In all such cases of dispute, between the biologists on one hand 

 and the petrographers on the other, every effort should be made to show 

 that the conditions under which the rock containing the supposed organic 

 remains was formed, were incompatible with one or the other view, instead 

 of leaving the question to the weight of aiithority. For example, while the 

 lithologist might insist for all time that these forms were produced by 

 alteration, and that he could trace every step from the beginning to the end, 

 the biologist might also insist that the forms were organic, and that he could 

 trace every step from the most perfect form to those whose structure had 

 been almost entirely obliterated by subsequent metamorphism. Both follow 

 the same series, but each one traces it out in the reverse way from the other. 

 Who shall decide between them ? Plainly this can only be done satisfactorily 

 by independent evidence which will disprove one side or the other. For 

 example, the mode of occurrence of some of the rocks in which Dr. 

 Carpenter found fossils, is that of eiaiptive bodies and veinstones ; therefore, 

 the proof of their origin decides the question, in these cases, adversely to 

 the biologist. 



The case of the eosoon affords another example of the successful appli- 

 cation of the above method of determining the nature of a disputed form. 

 It has been found by Professor Whitney and myself that limestone contain- 

 ing eosoon, acknowledged to be such by Carpenter, Dawson, and Hunt, cuts 

 off dikes running through the country rock ; thereby proving this eozotinal 

 limestone to be a later deposit than the country rock, or a veinstone. This 

 decides the case completely against the biologist, and removes from the 

 decision every element of ambiguity or theoretical reasoning ; since a vein- 

 stone formation of later date than the country rock is entirely incompatible 

 with the growth of an organism such as the cozooii is claimed to be.* 



In figure 6, Plate VIII., is shown one of the picrites in which the augite 

 appears on the right hand of the section. This mineral exhibits in places, 

 particularly at its base, a greenish alteration-product, and it incloses grains 

 of olivine fissured and partly altered to ser^^entine. The remaining portion 



 * Bull. Mus. Comp. Zo6l„ ISSi, vii. 538-338. 



