Pirsson and Washington — Geology of New Hampshire. 509 



with corresponding changes in the composition of the magmas 

 beginning with one of medium character, then changing to a 

 more femic type and then back to a corresponding more salic 

 one, and thus following the general history of differentiation 

 observed in other districts. The only objection against this 

 view which occurs to us is, that if the aplitic liparase injections 

 are the latest phase along the contact between the camptonose 

 and pulaskose rocks and contain blocks of the former, why do 

 they not contain blocks of the latter ? The answer to this is 

 twofold — first, we are not sure that they do not, we did not 

 observe them in the exposures studied ; and second, we do not 

 feel sure that we could identify them even if they were pres- 

 ent, because in the field the liparose and the lassenose of the 

 marginal facies both have the same aplitic habit and appear 

 very much alike. They differ chemically and somewhat min- 

 eralogically as has been described, but in the rock masses these 

 differences might not be appreciated and blocks of the one in 

 the other would certainly be difficult and perhaps even impos- 

 sible to recognize. 



Moreover in this connection it should be pointed out that 

 the dikes of liparase which penetrate the pulaskose were 

 nowhere observed to contain fragments of the latter although 

 of later intrusion into it, and it is in fact uncommon for aplitic 

 dikes to contain such masses of the granitic rocks they pene- 

 trate, although they sometimes do. The further discussion of 

 this point would carry us too far, but enough has been said to 

 show that the objection advanced is not necessarily decisive 

 against the sequence we have postulated and which we believe 

 is best suited to explain the facts observed. 



The Aplitic Marginal Facies 



The aplitic, persalic marginal facies of the main massif of 

 pulaskose is an interesting feature of the petrology of the area. 

 Aplitic border facies of granites are probably not uncommon 

 and have been described by a number of observers as listed 

 by Rosenbusch.* In these cases, however, this appears to be 

 mainly an endomorphic textural modification of the rock mass. 

 In the present case it is not only a textural but much more a 

 chemical modification, the border being richer in silica than 

 the rest of the massif. At first thought it might seem as if 

 the syenite had enriched itself in silica by solution of the envel- 

 oping rocks in some such way as Dalyf has recently suggested 

 for occurrences in Canada and elsewhere. A further consid- 

 eration of the subject, however, does not seem to favor this 

 view. It is true that the border facies contains here and there 



* Mass. Gest., 3d ed., 1895-6, p. 65. 

 f This Journal, xx, 1905, p. 185. 

 Am. Jour. Sci.— Fourth Series, Vol. XXII, No. 132.— December, 1906. 

 35 



