1 82 SIDNEY POWERS 



where a special mechanism for the transfer of heat from depth 

 exists for a relatively long period of time, as in a part of the 

 Ogunquit dike. 



The material worn from fragments during their rounding and 

 the cement which is dissolved from conglomerates appear in the 

 dike as xenocrysts. Thus, in the hand-specimen of the Rossland 

 dike many small fragments of quartzite and gneiss one-quarter of 

 an inch or less in length may be seen. In the Brevik (Sweden) dike 

 Hedstrom reports grains of quartz and feldspar of microscopic size 

 derived from the matrix of the conglomerate. In the Somerville 

 dikes numerous xenocrysts of quartz and andesine feldspar, which 

 have come in part from the inclusions, are found in the groundmass. 

 The Shelburne Point dike described by Hitchcock contains many 

 small fragments of the inclusion-rocks. 



The question of the fragmentation of rocks from the differential 

 expansion of the constituent minerals and the importance of the 

 inversion point of quartz are of bearing in quartzose inclusions only 

 in the cases where the inclusions have been heated to about 575° C. 

 The criteria of high temperature of the inclusions, at the time of 

 the chilling of the dike, are fused contacts or evidences of corrosion. 

 In part of the Ogunquit dike there is evidence of high temperature 

 and partial assimilation of the inclusions, most of which contain 

 only a small amount of quartz. This corrosion apparently pro- 

 ceeds by the fragmentation of the minerals, as xenocrysts are 

 exceedingly abundant in the dike-rock. In the Somerville dikes 

 the inclusions of feldspar and vein quartz show marked corrosion, 

 yet there is no sign of fragmentation at their peripheries. In the 

 Aschaffenburg dikes there has been a selective formation of xeno- 

 crysts of certain minerals as if the rocks had been disrupted by the 

 unequal expansion of the different minerals. 



In conclusion it may be stated that some knowledge concerning 

 the mechanism of dike-injection may be gained by the consider- 

 ation of the movements of the inclusions. Further observations 

 are needed concerning the possibility of circulation which will 

 cause inclusions of lesser specific gravity than the dike-magma to 

 descend in dikes. 



