670 HENRY S. WASHINGTON 



find discrepancies, due to differences in the process of differ- 

 entiation. 



At Magnet Cove we have, without any doubt, the results of 

 the differentiation in place of a small body of magma. This 

 particular mass may have had originally the composition of the 

 magma underlying the whole region, or it may have been itself 

 a differentiate of this. Differentiation in such a large body of 

 magma as that underlying the whole igneous region of Arkansas 

 would naturally be likely to give rise to diverse products at 

 different points, in which, however, could still be traced some 

 of the original general characters of the whole. We are as yet 

 scarcely in the position to deal with such intricate and obscure 

 problems, but the results of Pirsson's investigations and of those 

 embodied in the preceding pages seem to furnish a promising 



means of attack. 



Henry S. Washington. 



