416 The American Naturalist. [May, 



mental character, and in some cases there are indications of violent 

 explosive action. This is quite in accord with the nndesitic nature 

 of materials thrown out, which are of types common in the Pacific 

 region. As to the age of the rocks, it would be idle to speak until the 

 evidence of their organic contents has been duly set forth ; but it 

 would undoubtedly be very rash to refer them all to a recent age, ami 

 some of them may be found to go back far into the Tertiary times. " 



Geological News— General.— Several fossils collected by M. 

 Griesbach while exploring the Central Himalayas closely resemble 

 those found in the corresponding Alpine beds. In view of this fact, 

 the Academy of Sciences of Vienna has decided, by an agreement with 

 the Indian Government upon an exploration of the Central Himalaya 

 region in order to compare its geology with that of the Eastern Alps. 

 M. Diener, president of the Alpine Club of Vienna, will take charge 

 of the expedition. {Revue Scientifique, April, 1892.) 



MINERALOGY AND PETROGRAPHY. 1 



Petrographical News.— One of the most valuable contribution* 

 to American petrography that has yet appeared is that volume of the 

 Arkansas Geological Survey Report that treats of the eruptive rocks 

 of the State. In it the late Dr. J. F. Williams' 2 gives an excellent 

 account of the little-known but very interesting eleolite and leucite 

 rocks that occur as bosses and dykes in Pulaski, Saline, Hotsprings, 

 Garland and Montgomery Counties. It would be well worth the 

 while to give a full abstract of the author's careful investigation of 

 these extremely rare rock-types, but space allows merely a reference to 

 the mere outline of his work. Especial importance is attached to the 

 study of the eleolite syenites at the present time, particularly where its 

 plutonic and dyke forms occur together, since Rosenbusch has 

 recently prophesied the existence of a group of dyke forms which be 

 calls monchiquites, that will be found to occupy a position among the 

 eleolite rocks corresponding to that held by the camptonites. among the 

 plagioclase rocks. The age of the Arkansas eruptives is pr< 

 Cretaceous. In Pulaski County they form the main mass of Fourche 

 Mountain. The most abundant variety here is that locally known as 

 'blue granite.' It is a granitic porphyritic rock in which the 



1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 



