CONSTITUTION AND ORIGIN OF SPHERULITES 
IN ACID ERUPTIVE ROCKS. 
BY 
Whitman Cross. 
[Read before the Society, April 25, 1891.] 
In the course of geological investigations in Colorado, ex¬ 
tending through several years, the writer has observed a 
number of occurrences of rhyolitic rocks containing the in¬ 
teresting bodies known as spherulites and lithophysse. Some 
of these occurrences have furnished material remarkable for 
its variety and degree of development, and exhibiting in 
unusual clearness certain important characteristics of these 
structural forms. The author began the study of these 
spherulites without having had previous experience with 
such objects, and he naturally sought to apply to them the 
classificatory scheme and the descriptive terms of the lead¬ 
ing authorities of the day; but, whether he turned to the 
German, to the French, or to the English school of petrog¬ 
raphy, he found that the current views regarding spheru¬ 
lites were in large measure inapplicable to the case in hand, 
and that the schemes of classification were unsatisfactory. 
A full description of the spherulitic rocks collected in Col¬ 
orado is being prepared for publication by the U. S. Geologi¬ 
cal Survey, and it is the intention to give at the present time 
only such results of the investigation as have a general bear¬ 
ing upon the subject and tend to corrrect certain inaccurate 
or fallacious beliefs concerning spherulites which are current 
in text-books and in general literature. Preliminary to this 
discussion it will be necessary to review in brief the origin 
of the prevailing ideas. 
53—Bull. Phil. Soc., Wash., Vol. 11. 
(411) 
