Pirsson and Washington — Geology of New Hampshire. 497 



In the mode the orthoclase and part of the olivine of the 

 norm have united to form biotite, while the hornblende of the 

 mode is made up from some of the normative olivine, diopside, 

 magnetite and anorthite and probably it contains some or all 

 of the nephelite as well. This is only another illustration of 

 the complex nature of the hornblende molecule. 



The mode is thus abnormative, containing a notable amount 

 of hornblende and some biotite. The fabric, as has been 

 shown, is granular and pseucloporphyritic or poikilitic. If 

 one wished to characterize all of these features in the name 

 it would become biotitic hornblende-grano-phyro-camptonose, 

 but more simply it is hornblende-poikilo-camptonose. As, 

 however, the fabric and other characters of the rock are so 

 peculiar and striking, it has been thought best to erect this 

 rock into a distinct type, on which the name of gilfordal 

 camptonose is bestowed, the type adjective being derived from 

 the village of Gilford near the type locality. 



Classification in the older systems. — In these, if one con- 

 siders merely the qualitative statement of the chief minerals 

 of the rock, that it is composed mainly of plagioclase and 

 hornblende, it would be termed a diorite ; if we take into 

 account also its basic chemical character, and the large amount 

 of lime, iron and magnesia, it would be considered rather a 

 hornblende gabbro ; if there is also considered the nature of 

 the hornblende, the presence of the pyroxene and biotite and 

 the association of the rock with alkalic syenites and with 

 camptonites and its close chemical and mineral correspondence 

 with the latter, it would fall in Rosenbusch's family of essex- 

 ites. It has, it is true, less alkalies than most of these rocks 

 show, but it is also to be noted that under the heading of 

 granular rocks, composed chiefly of basic plagioclase and 

 brown barkevikitic hornblende, associated with alkalic rock 

 complexes, types which differ quite widely among themselves 

 in various chemical features have been grouped as essexites. 

 This is seen, for example, in the table of analyses in Eosen- 

 busch's Elemente der Gesteinslehre and our analysis agrees in 

 each of its features with some of those there given. 



Fades of the grano-camptonose (essexite) mass. 



At the southwest foot of Locke's Hill the bench, which 

 along the western side forms the top of the camptonose area, is 

 cut off by a ravine, and at this point, as previously mentioned, 

 both it and the pulaskose (syenite) are in contact with the 

 gneisses. Above this on the bench are outcrops forming line 

 exposures of the salfemic rocks, and it may be seen here that 

 locally the camptonose passes into phases of an even granular 



