GEOLOGY 01' THE WHITE MOUNTAIN DISTRICT. 1 79 



andalusite slate starts from Mt. Willey, pursues a course N. io° E. to the 

 railroad, thence climbs Mt. Willard about N. 75° W., and back of the Field 

 spur changes to N. 10° E. again, crosses Cascade brook, and after reach- 

 ing a very great altitude suddenly terminates. It is flanked on both sides 

 for a considerable part of its course by the Albany granite. If this was 

 a stratified rock, we should say that the structure of the slates was that of 

 an inverted synclinal, underlaid regularly by this constant inferior mem- 

 ber. In the present state of our knowledge of altered and eruptive rocks, 

 it cannot be said that these underlying granites are certainly not sedi- 

 ments, so thoroughly metamorphosed as to have lost their lines of orig- 

 inal bedding. The evidence in favor of their eruption, since the deposi- 

 tion of the andalusite slate, is increasing. 



In the preceding description of the slates, I may have stated too 

 strongly their apparent distinctiveness as a formation from the neigh- 

 boring rocks. This is the impression one gets from their examination in 

 the field, uninfluenced by theoretical considerations. If we carry the 

 theory of metamorphism to an extreme, it might be said that the slates 

 could be altered into a granite by hydrothermal influences. If both rocks 

 contain essentially the same elements, it is conceivable that the fusion of 

 the dark slate might produce the spotted or the Conway granite. The 

 slate is penetrated largely by andalusite, a mineral devoid of alkali. If 

 either of the granites has resulted from the fusion of the slate, it is 

 plain the latter must contain considerable potash, else feldspar could 

 not be readily formed in the great abundance which is everywhere ap- 

 parent. Some analyses will be made of the slates in order to ascertain 

 whether an alteration of this andalusite slate into granite be possible.* 



Two considerations may be stated which incline to the belief that the 

 slates constitute an independent formation, and have not undergone met- 

 amorphosis. First, in comparing together the courses of the strata back 

 of Mt. Willard, and the spur of Mt. Field, it would seem as if the slates 

 had been violently bent into their present trend by the subsequent erup- 

 tion of the spotted granite crowding into their eastern flank. The slates 

 are twisted and broken in many places, the fragments being cemented 



* The results of one analysis show a deficiency of silica in the slate instead of alkali. This agrees with 

 the results of numerous recent analyses of the Cornwall killas by J. Arthur Phillips — Quar. jfoiir. Geol. Soc, 

 Aug., 1S75. He also insists that the granites are not derived from the metamorphosis of the slates. 



