•_'7t'> Pirxson and Rice — Geology of Tripyramid Mountain. 



upward according to the arrangement shown in tig. 4. On the 

 east side of the mountain the rocks occur in the same order 

 ascending from Sabba Day Brook. Lahradorite rock occurs 

 on this stream also, on the authority of his assistant, Prof. J. H. 

 Huntington, and is in contact with granite of the Conway 

 type. 



The occurrences and contacts as seen appealed to Hitchcock 

 as irruptive ones and he suggests clearly that the syenite is an 

 eruptive mass ; but, influenced by the theoretical views pre- 

 viously mentioned, he attempts to classify ossipite (gabbro) and 

 porphyritie granite as "formations" with the equivalence of sed- 

 imentary beds.* Through, and upon these, if we understand 

 his view correctly, successive layers of syenite were poured out 

 and the whole then slightly folded. Thus the section is drawn as 

 given and he considers the mountain to be a syncline in its 

 structure. Leaving aside this interpretation, which in light of 

 our present knowledge is impossible, and with a minor change, 

 we shall show later that Hitchcock's idea of the general struc- 

 ture of the mountain is a possible one which must be consid- 

 ered in any discussion of its geology. 



Geology. 



Our geological field work within the area shown on the map 

 has been confined to the western two-thirds, including the 

 north and south slopes of Tripyramid, traverses of its crest line 

 and exploration generally of the western half of the area. 

 The ridge leading southeast from Tripyramid to Whiteface 

 Mountain, beyond the limits of the map, has also been traversed ; 

 but combinations of want of time, bad weather and lack of 

 camping equipage have prevented us from exploring the lower 

 eastern slopes of the mountain in the valley of Sabba Day 

 Brook and we have here been obliged to fall back on the obser- 

 vations of Prof. J. H. Huntington, as given in Hitchcock's 

 report and mentioned later. The manner in which the geology 

 is concealed and the difficulty of traversing parts of the area 

 have been already alluded to, and one might say here that the 

 true penological history of large areas of the White Mountains 

 cannot, under existing conditions, be adequately deciphered, the 

 covering of glacial drift, debris and vegetation is so complete. 

 Most interesting problems are suggested by many exposures and 

 occurrences, but the data for their solution cannot be obtained. 



What we have learned concerning the area covered by the 

 map is put down upon it and the conclusions we have drawn 



* Later (op. cit.. vol. II, p. 667) Hitchcock appears to have considered it 

 possible that the gabbro was eruptive and that the "Labrador formation" 

 may not exist in New Hampshire. 



