Pirsson and Bice — Geology of Tripyrarnid Mountain. 285 



clinal folding, Hitchcock's section suggests one interpretation 

 for the structure of Tripyrarnid which at first thought appears 

 possible, that is, it may consist of successive layers of gabbro, 

 monzonite and syenite erupted through the granite and on 

 top of one another in the order named, and beneath some cover 

 which has since disappeared, with the semblance to a sedimen- 

 tary succession. 



We do not believe this view is tenable ; it is negatived by 

 the character of the contacts, which where visible are vertical 

 or approximately so, by the dome-jointing, and by the direc- 

 tion of the contact between the monzonite and syenite on the 

 North Slide, which in this case, instead of striking diagonally 



Fig. 5. 



V.f:'. *".*■»■ 'v.*""""' ♦**+■»♦♦ , f t -*V* 



*tvVv v uvV, : '.V::';. 



"', ftr / i\ «in ;£$£; 





Fig. 5. 

 before. 



Inferred geological map of Tripyrarnid intrusion. Legend as 



down the slope to the west, as it does, should follow round the 

 mountain on a contour line. 



The sequences referred to suggest very naturally that Tri- 

 pyrarnid is a differentiated mass of igneous rock, and, as has been 

 found to be so commonly the case elsewhere, it begins with an 

 onter basic border, succeeded by a less basic inner part which 

 in turn gives way to an acid interior core. If we take into 

 account the facts as observed and imagine to ourselves the 

 geology of bed-rock that would be exposed if all the overlying 

 material should be removed, we should have the relations shown 

 in fig. 5, adjoining. In this, the southeast corner has been left 

 indefinite for the reason, previously stated, that we do not know 

 whether the Tripyrarnid mass is definitely cut off from that of 

 Mt. Whiteface by the granite, or not. It is to be understood 

 that these boundaries are not to be taken in a hard and fast 

 way, as representing everywhere what we believe to be the 

 exact location of definite geological contact lines. They only 

 show in a general, or diagrammatic, manner what we believe 



