234 CALIFORNIA ACADEMY OF SCIENCES. 



sists of both hypersthene and augite, but the hypersthene rather 

 predominates. Its determination as such rests upon its pleochro- 

 ism and its orthorombic character, as shown by the extinction 

 of light parallel to its principal axis. This occurrence of hypers- 

 thene, as a rock constituent, adds another to the already wide- 

 spread range of this mineral, which has suddenly jumped into 

 prominent existence in such a remarkable manner, through the 

 brilliant discovery of Mr. Whitman Cross*, and the subsequent 

 investigations of Messrs. Haguef and Iddings. 



Analysis No. 1, made by Mr. R. W. Woodward, then of Yale, 

 is of the younger and more vesicular rock, and Analysis No. II, 

 made in the Laboratory of Harvard College, is of the more 

 compact variety. 



SiO., 55.89 5G.33 



Al/5 3 2001 20 - 19 



Fe 2 3 1.77 7.1G 



FeO 4.72 



MnO 06 



CaO 8.12 8.74 



MgO 4.57 2.53 



Na 2 2.66 3.81 



K 2 2.29 1.38 



Ignition 19 



"o' 



100.28 100.14 



The low percentage of silica, and the constant presence of 

 olivine, would seem to keep this rock within the line separating 

 basalt from hypersthene-augite-andesite. 



* On Hypersthene Andesite; Ant. Journal of Science, February, 1883. 



t Notes on the Volcanoes of California, Oregon, and Washington Territory; Am. Journal 

 of Science, Sept. 188?; and Notes on the Volcanic Rocks of the Great Basin; Am. Journal of 

 Science, June 18S4. 



