58 PROCEEDINGS OF THE CHICAGO MEETING 



Hall at 3.40 o'clock, Wednesday afternoon, under the chairmanship of 

 Vice-President Willet G. Miller, with Edmund Otis Hovey serving as 

 secretary. The first paper read was entitled 



A SIGNIFICANT PETROGRAPHIC UN(X)NFORMITY 

 BY CHARLES P. BERKEY 



(Ahstract) 



Just as in the field of stratigraphy great reversals of the regular course of 

 sedimentary development are indicated by misfit structures, so also is it in 

 the field of petrology ; but the nature of the evidence differs greatly and the 

 method of investigating and the interpretation criteria belong by common 

 consent to a branch of the science not usually credited with historical bearing. 

 Some of these reversals in rock development and transformation are not re- 

 corded at all in stratigraphic form. 



It is possible also that the paleopetrologist, or the man who reads the ancient 

 history of rocks, may add to the understanding of the significance of the ordi- 

 nary unconformities. 



Read from manuscript. 



ROCKS OF KOTIALA AND KEA, HA^YAII 

 BY HENRY S. WASHINGTON 



(Abstract) 



The Kohala Mountains, at the northern end of Hawaii, are the ruins of the 

 oldest of the five volcanoes on the island. So far, the lavas of this center have 

 been but little studied. The present paper is based on material collected in 

 September, 1920. 



The lavas of Kohala, for the most part, belong to two types of andesine 

 basalt or oligoclase andesite, the hawaiite and kohalaite of Iddings. One is 

 densely aphanitic and aphyric, and the other porphyritic, with many pheuo- 

 crysts of plagioclase. The new analyses made indicate that, while at Kohala 

 there is little dilference between them, yet the lavas of this volcano, on the 

 whole, are distinctly more alkalic than those of the recent volcanoes, Mauna 

 Loa and Kilauea. 



The study of the lavas of Mauna Kea is based chiefly on material from the 

 lower slopes, especially from the lowest flows exposed in ravines along the 

 ct)ast, and not heretofore collected or studied, supplemented by Daly's study 

 of lavas from the upper parts of the volcano. The lavas mostly fall into two 

 types similar to those of Kohala and are similar chemically ; they do not sup- 

 port Daly's suggestion of gravitative control at this volcano. A recent lava 

 at sealevel has a composition almost identical with one collected by him from 

 the summit. The analyses show that there is comparatively little difference 

 in composition throughout. The paper is preliminary to a more general study 

 of the lavas of Hawaii and the other islands of the group, based on recent 

 collections made by the author and others. 



Presented without nianuscri2:)t. 



