EVIDENCE SUSTAINING DYNAMIC HYPOTHESIS. 131 



1. The gneissic character of the microstructure as traced from the coarse grained 

 through the ellipsoidal to the streaked varieties. The augen-structure represented 

 in specimen number 160 is clearly typical of the results usually credited to dynamic 

 movements. Inasmuch as this appears to be merely a special development of a 

 portion of the rock having little or no augite, it would not seem unwarranted to 

 infer that the agencies operating here affected other portions of the rock as well, 

 and hence that the development of the gneissic structure was. in both cases refer- 

 able to the same agencies. 



2. The evidence of recrystallization of the granular areas. This appears not 

 only in the irregular interlocking outline of adjacent grains, but the frequent pres- 

 ence of fresh plagioclase feldspar as a cement for the other constituents and the 

 development of hornblende in idiomorphic forms in the more gneissoid rock. 



3. The indication of dynamic action as shown {a ) by the fracturing of the augite 

 and microcline grains, and (6) the indication of strain appearing in the bending of 

 the microcline lamellae, accompanied by undulatory extinction and the develop- 

 ment of polysynthetic twinning of the pyroxene. These phenomena are chiefly 

 confined to the coarse grained rock, and even here are not pronounced. It may 

 be that some of them are due to movements subsequent to the development of the 

 gneissic structure. The appearance of strain in the microcline, however, in certain 

 cases (page 116) seems rather to be connected with the production of the gneissic 

 structure. This is true also in certain cases in the breaking of the pyroxene 

 grains, but in general neither pyroxene nor microcline furnish any evidence as to 

 what proportion, if any, of the granular materials represent fragments of the orig- 

 inal minerals. 



4. The character and relations of the inclosed apatite. The significance of these 

 deposits lies in their generally crushed condition. The crushed appearance of the 

 apatite is more pronounced, so far as the limited data at hand shows, in the de- 

 posits occurring in the streaked gneiss than in those in the coarser rock. In places 

 wlrere the gneissic structure of the rock is imperfectly developed, the crushing of 

 the apatite likewise appears incomplete. The mass is made up of rather coarse 

 fragments, with granular apatite filling the interstices. In some cases (page 107) 

 the mass is intersected by thin seams of feldspathic material extending in from the 

 walls and continuous with the surrounding layer. Often the deposit is reduced 

 almost wholly to a granular condition. These granular deposits, called sugar apa- 

 tite, are sometimes of considerable extent, as noted by Professors Penrose * and 

 Harrington, t 



Professor Penrose says: "The granular variety known as sugar apatite is of a 

 white or pale green color and looks like coarse sand, more or less coherent. * * * 

 It is one of the purest forms of apatite mined. It is uncertain what could have 

 caused the apatite to assume this granular condition." 



Professor Harrington states that ''though at some localities the apatite occurs 

 chiefly in crystals, at others it is wholly or almost altogether massive, varying from 

 compact or crypto-crystalline to coarse granular. Frequently also it exhibits a dis- 

 tinct lamellar texture. A friable saccharoidal variety is very common and often 

 termed ' sugar phosphate.' When white it is sometimes difficult to distinguish by 

 the eye from some forms of quartz sandstone. * * * Crystals are sometimes 

 imbedded in this granular apatite, and frequently also rounded masses of apatite 



*R. A. F. Penrose : Bull. 46, U. S. Geol. Surv., p 38. 

 •j- B. J. Harrington : Geol. Survey of Canada, p. 14 G. 



