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PETROLOGY: H. S. WASHINGTON 
the symbol sacred to his village (gens), there was no attempt to coerce 
the child to observe any rite or to direct its mind to think upon tribal 
beliefs. 
A child gifted with an inquiring mind would be apt to ask questions 
concerning the symbols and the customs attending them of his father 
or mother and if his parents belonged to the thinking class, they might 
put the child's thoughts on the trail that in time would lead him to a 
knowledge and an understanding of the rehgious beliefs expressed in 
the tribal rites, otherwise, the boy or girl would grow up in unques- 
tioning ignorance of the truths hidden within the dramatic rites of 
the tribe. 
The sacred legend of the Omaha lays stress upon 'thought.' 'And 
the people thought,' was always the prelude to any change for the 
betterment of the tribe. The Indian thinker became the Indian seer, 
but, the man must seek for himself the path to that height. 
THE CORRELATION OF POTASSIUM AND MAGNESIUM. 
SODIUM AND IRON, IN IGNEOUS ROCKS 
By Henry S. Washington 
GEOPHYSICAL LABORATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Presented to the Academy, October 29, 1915 
In its modern development the science of petrology is devoted, in 
great part, to the physico-chemical study of igneous rocks, regarded as 
congealed solutions, and of the conditions of separation of their constitu- 
ent minerals. Distinct from, and in some respects more general than, 
this, is the study of the distribution of the chemical elements of which 
they are composed. 
This distribution may be spatial; that is, according to the occurrence of 
groups of rocks, or rock series, over different areas of the earth, each with its 
dominant chemical characters. Such districts are known as petrographic 
provinces or comagmatic regions. Their study involves the considera- 
tion of the original homogeneity or heterogeneity of the globe, as well 
as, possibly, certain tectonic factors, as suggested by Harker, Becke, 
and others, and does not concern us here. 
Or the distribution may be according to a chemical correlation, ex- 
pressed by the presence of certain pairs or groups of elements, which 
vary together, however they may be spatially distributed. In other 
words, in rock magmas, solidified as igneous rocks, as well as in their 
constituent minerals, certain of the elements are found to be generally 
and persistently associated together, the one being abundantly present 
