32 
MUSEUM BULLETIN NO. 2. 
passed, and in part assimilated by the rising magmas. The 
magmas would also probably assimilate some of the enclosing 
Purcell sediments but not enough to materially affect their 
composition. 
The simple sills solidified in the u ual manner of such intru- 
sives, while the acid material differentiated under the influence 
of gravity giving rise to composite sills. 
