yb NEW YORK STATE MUSEUM 



It is quite possible that much or all of the pressure within the 

 intruding magmas was simply " shouldering pressure exerted (by 

 the magmas) on the adjacent rocks under bathylithic, or deep- 

 seated, conditions " as suggested by Gushing. 



The gabbro and diabase. As already stated, the interior por- 

 tions of most of the gabbro stocks are nonfoliated and they pos- 

 sess a diabasic texture, while the outer portions are usually highly 

 foliated rocks, often true amphibolites. More or less granulation 

 is common as seen in the thin sections. In many places the degree 

 of foliation varies considerably within single stocks, a very fine 

 example already having been described as occurring on the little 

 hill just south of North pond (see page 58). The foliation shows 

 a strong tendency to box the compass around the borders of the 

 stocks, and, therefore, often strikes across the structures of the 

 older adjacent rocks. If due essentially to regional compression 

 after the solidification of the gabbro, should not the foliation every- 

 where strike at least approximately at right angles to the direction 

 of application of the pressure? Also, how are the notable varia- 

 tions in foliation and granulation to be explained on the basis of 

 regional pressure ? 



It is believed that the foliation and granulation of the gabbro 

 stocks are largely, if not wholly, primary features due to move- 

 ments in the magma- before final consolidation. Considerable pres- 

 sures must have obtained within the stock chambers while the 

 magmas were being intruded under deep-seated conditions. Such 

 pressure against the country rock, combined with the development 

 of difirerential flowage particularly in the magmatic borders, would 

 readily account for the peripheral foliated zones which were, no 

 doubt, produced during a late stage of magma consolidation. But 

 the conditions of magmatic pressure and flowage must have varied 

 considerably, and thus the local variations in degree of foliation 

 and granulation are accounted for. 



Certain of the diabase dikes which cut the Marcy anorthosite 

 in the vicinity of Blue Ridge village are also more or less foliated, 

 their borders particularly so. As in the gabbro stocks, so here, the 

 foliation is considered to have been due to differential magmatic 

 flowage under moderate pressure during a late stage of magma 

 consolidation. In these dikes, however, the foliation was developed 

 parallel to the strike of the dikes because cross-sections of these 

 magma chambers were long and narrow rather than rounded or 

 elliptical as in the gabbro stocks. 



