62 cross: lavas of Hawaii 



rocks have a pronounced regional distribution on the earth, which 

 maybe appropriately expressed by the names Atlantic and Pacific 

 branches or kindred, and (2) that the chemical differences of 

 these groups are genetically connected with the tectonic distinc- 

 tion made by Suess between regions of subsidence due to radial 

 contraction and zones of folding due to tangential stress. The 

 study is not yet complete but the principal results may be fore- 

 cast. 



In this review of Hawaiian lavas the literature has been care- 

 fully studied; an extensive collection of rocks from Oahu and 

 Hawaii, made by Prof. C. H. Hitchcock for the U. S. National 

 Museum and not previously described, has been examined, 1 and 

 also a collection from the islands of Kauai, Maui, and Hawaii, 

 made by the writer. The chemical discussion is based on 36 

 apparently reliable analyses, 11 of which have been made by 

 chemists of the U. S. Geological Survey, of rocks of the writer's 

 collection. 



Character of Hawaiian lavas. — The lavas of the Hawaiian vol- 

 canoes are generally basaltic in habit and have received far less 

 attention than they deserve. As indicated by the work of Cohen, 

 E. S. Dana, Lyons, and Silvestri the rocks range chiefly between 

 normal basalts rich in olivine, augite, and highly calcic plagio- 

 clase, to pyroxene andesites, either free from or poor in olivine, 

 and containing andesine or more richly sodic plagioclase. There 

 are, however, still more basic rocks than normal basalt, such as 

 tephrite, limburgite, nephelite, and melilite basalt, while one is 

 practically an effusive peridotite similar to wehrlite in compo- 

 sition. At the other extreme there are magmas of essexitic or 

 trachydoleritic character and some andesites nearly free from 

 pyroxene. A soda trachyte described by the writer in 1905 is 

 the most siliceous and feldspathic rock. 



The existing analyses evidently do not cover the entire range of 

 rock types but classifying the analyzed rocks in the quantitative 

 system they are found scattered through 3 classes and belonging 

 to 14 subrangs, namely: Nordmarkose-Umptekose (I-II.5.1.4.), 

 akerose (II. 5. 2. 4), andose (II. 5. 3. 4), beerbachose (II. 5. 3. 5), 



l The writer's thanks are due to Dr. G. P. Merrill for this opportunity. 



