4 THE JOURNAL OF GEOLOGY. 



naturally suggested a comparison of these rocks with those of 

 similar character in the Boston basin and eastern Canada, as well 

 as a further search for other regions of the same kind. This 

 search has already proved successful in North Carolina and 

 Maine, while an examination of the older literature indicates 

 many other places where a recurrence of like conditions may be 

 confidently expected. 



The proper interpretation and areal mapping of all the 

 demonstrably volcanic regions in the Appalachian crystallines 

 will not only afford much material of interest in the study of 

 petrography and dynamometamorphism, but will also contribute 

 to the differentiation and final understanding of the vast belt of 

 diverse crystalline rocks to which they belong. 



DIVERSITY OF OPINION REGARDING ANCIENT VOLCANIC ROCKS. 



There is notable in the different countries where geology 

 is cultivated a wide diversity of opinion regarding ancient vol- 

 canic rocks. In some regions such rocks have been entirely 

 overlooked or else misinterpreted ; in others they are recognized, 

 but are conceived as having been formed under circumstances so 

 different from those which now obtain that they are genetically 

 and inherently distinct from the products of modern volcanoes ; 

 in a few only are they considered as having been origin- 

 ally identical with recent effusive rocks, and as differing from 

 them only in alterations due to subsequent causes. This diver- 

 sity of opinion may be accounted for in part by the varying state 

 of preservation of ancient volcanic material in different parts of 

 the earth's surface or by the lack of experience of field geolo- 

 gists with the characteristic features of modern lavas. It is, 

 however, also due in a measure to the persistence of certain 

 ideas promulgated by early masters of the science in their 

 respective lands. 



It was in Great Britain that the real nature of ancient volcanic 

 products received its earliest and fullest recognition. In spite 

 of the absence of active volcanoes from the islands, these rocks 

 have from the earliest days of geological inquiry been favorite 



