508 Pirsson and Washington — Geology of New Hampshire. 



magmas upward into the mass of pulaskose and into the sur- 

 rounding area where they appeared as dikes, except in one 

 place on the northwest boundary where the magma formed a 

 small stock. In the dikes the texture assumed was dense and 

 more or less porphyritic, forming trachiphyro-camptonoses 

 and akeroses (camptonites and spessartite), but in the stock the 

 crystallization was coarser, producting a granular texture and 

 making grano-camptonose (essexite). This assumes that the 

 rocks of the dikes and of the stock have a similar composition ; 

 that this is so, has already been shown with respect to the 

 camptonoses. In regard to the akerose dikes it has been 

 shown also that they correspond to one facies of the stock, 

 which is somewhat variable in its composition. 



The injection of the camptonose magma evidently was not 

 everywhere a simultaneous one, for we find dikes of it in finer 

 textured types cutting the camptonose stock, proving that this 

 had already cooled and solidified to depths now exposed by 

 erosion, when these later upth rusts of this magma took place. 

 It is thus quite possible that the dikes of camptonose seen else- 

 where are not all exactly of the same age but that their injec- 

 tion was successive, some corresponding in age with the intru- 

 sion of the stock and some later, like those dikes which cut it. 

 On the general principles of differentiation as thus far devel- 

 oped, it would also seem probable that the akerose (spessartite) 

 dike cutting the summit of Mt. Belknap was one of the earliest 

 of this set, since it is less differentiated. 



Following these came the period of the injection of the 

 liparase (aplite), the persalic differentiate complementary to 

 the camptonose. This has formed dikes in the puiaskose and 

 in the camptonose stock. In the latter case it has brought up 

 pieces of the camptonose in its various textural modifications 

 and of the enveloping schists and gneiss involved within it, and 

 in one place it forms an irregular mass, the breccia already 

 described. At the time of its injection, cooling in and about 

 the stock was becoming more pronounced and the magma was 

 quite viscous. This is shown by the shattering and rupturing 

 it produced on its upward way along the rock walls, the frag- 

 ments thus broken off becoming kneaded through the mass, and 

 also by the fact that these fragments were not melted, absorbed 

 or changed, even when small and angular in shape. This was 

 the final event in the formation of the igneous rocks. 



The sequence thus worked out would be more certain if the 

 actual contacts were everywhere visible, but as already stated 

 they are in great part covered with drift. It however seems 

 to correlate best all the facts seen in the field and determined 

 by the laboratory studies. Moreover it has the advantage of 

 simplicity in that it requires only three periods of injection 



