180 WILLIAM J. MILLER 
LACK OF VARIATION OF THE DIABASE 
Because of its remarkable homogeneity in composition, the 
diabase presents a marked contrast to the neighboring gabbro. 
The diabase never contains inclusions and never shows any evidence 
of magmatic assimilation even in the largest masses. This dif- 
ference is quite certainly due to the difference in the mode and 
condition of intrusion, the diabase having clearly been forced 
through comparatively narrow fissures in the country rock and 
pretty near the earth’s surface as the texture shows. In such 
intrusions magmatic stoping would be reduced to a minimum or 
absent. 
