2l6 REVIEWS 



America, and also with a valuable list of papers in which points of 

 resemblance between ancient and modern acid volcanic rocks have 

 been emphasized, and those treating of devitrification and of spher- 

 ulites. The paper is well illustrated by twenty- eight plates and is a 

 valuable contribution to our knowledge of ancient and more or less 

 metamorphosed volcanic rocks. 



The restriction of the prefix apo to those altered rocks that origin- 

 ally contained glass, leaves unsatisfied the demand for a general term 

 which can be applied to all more or less metamorphosed lavas that 

 once corresponded to unaltered rhyolites, basalts, andesites, etc., 

 whether glassy or holocrystalline. In this case it would seem advisa- 

 ble to adopt the prefix eo, proposed by Nordenskjold' without 

 regard to any particular age, indicating simply that the altered rock 

 had originally been what the remainder of the term signifies. In this 

 sense the volcanic rocks of South Mountain might be called eorhyo- 



lites and eobasalts. 



J. P. Iddings. 



' Ueber archceische Ergussgesteine ausSm&land. Bull. Geol. Instit., Upsala, No. 2., 

 Vol I., 1893. 



