394 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



It is obviouB that one of these rocks must be granite and the other gneiss. 



Again, it is said regarding the arrangement of the feldspar in the 

 " Porphyritic gneiss or granite," that 



" sometimes the crystals are placed in the rock with their longer axes parallel 

 to each other, and this plane is coincident with that of the strata; On the con- 

 trary there is often no arrangement to correspond with the stratification 



In 



our explorations no distinction has been made between tliem. The assump- 

 tion has been that the agencies producing the granite operated with greater 

 intensity, so as to induce a party condition in the mass, and obliterate the strati- 

 fication without destroying the porphyritic aspect of the rock. If the differ- 

 ence in condition involves radical distinctions in the mode of origin or in the 

 time of the fusion, then there are two formations to be considered instead of 

 one. But in that event the second rock was derived from the first, so that the 

 assignment of both to one group at present will not lead to error in respect to 

 the geographical areas occupied by the porpliyritic rock. .... Bcin<'- re- 

 garded as granite, no pains were taken to observe lines of stratification in it 



which doubtless exist The determination of the dip of this rock near 



the wing road station has been a difficult matter. There are jointed planes, 

 with scarcely any inclination that might be taken for strata. At the sugges- 

 tion of Dr. T. Sterry Hunt, a crystalline arrangement of materials dippin<^ 

 75° S. 40° E. was decided upon to represent the strata." (Geology of New 

 H'-mpshire, 11. pp. 98, 99, 102, 274.) 



In the same work, pages 472, 513, 514, Mr. J. 11. Huntington says of 

 the porphyritic gneiss : 



" The fact that rounded fragments of a dark gneiss are found in the porphy- 

 ritic shows that the porphyritic rock in Fitzwilliam is either iutrusive, or that 

 in the process of metamorphiara these fragments were not obliterated, and that 

 the dark kmeiss — which is very limited, but resembles some varieties of the 



-is the older rock." 



Bethlehem gneiss 



He further points to the fact that the Oonoord granite at Fitzwilliam 

 was intrusive. (/. c, p. 513.) 



Mr. Huntington also informs us that the " Concord" granite (Mont- 

 alban gneiss of Hunt) at Granby, Vermont, is distinctly eruptive, being 

 seen in contact with a mica schist, sending tonguep into the schist and 

 including fragments of it. 



After reading the speculations and conclusions given above, it is some- 

 what interesting to peruse the following from Prof. Hitchcock's pen : 



"It has been our constant aim to so divorce the facts and theories, irom each 

 other in the descriptions, that those who hold different general views from our 

 own will not find the observations unwarrantably obscured by individual spec- 

 ulations If our interpretation fails in anv narticular it Mali be in the 



I' 



