502 Pirsson and Washington — Geology of New Hampsh 



ire. 



The mode is abnormative and hornblende is the critical 

 mineral. In texture the rock is trachytic though not of a 

 typical character ; in fabric it is megaporphyritic and hence 

 it may be termed a hornblende-trachiphyro-camptonose. In 

 the prevailing systems the rock is a typical, fine-grained camp- 

 ton ite. 



To distinguish this alferphyric type of the camptonose and 

 other closely related magmas, characterized largely by the 

 abundance of highly automorphic, brown hornblende pheno- 

 crysts, and which rocks are called camptonites in the prevail- 

 ing systems, we propose the adjective hampshiral, from the 

 name of the state (New Hampshire) in which these rocks are 

 common and where the first typical camptonite was found by 

 Hawes. The general habit of these rocks may, therefore, be 

 described as hampshiroid. 



Variations from the hampshiral type. — Some of the black 

 salfemic dikes are precisely similar to the type described 

 above, but in other cases along with the hornblende there is 

 developed a considerable amount of a pale brown augite of 

 large extinction angle, well crystallized and appearing only in 

 the phenocryst stage of development. When this appears the 

 amount of plagioclase is lessened and a good deal of a cloudy, 

 faintly doubly refracting base is present, which may perhaps 

 be nephelite. It would seem as if lime had gone more 

 largely into the augites and less was left for plagioclase. In 

 one case wmere augite was quite abundant, no feldspar was 

 seen. These variations in mineral development may be seen 

 in closely contiguous dikes, as at Smith's Neck, and they are 

 not believed to be correlated with any notable change in 

 chemical composition. In a few cases there is also a variation 

 in texture, the grain becoming so densely fine that under a 

 high power the rock is made np of an exceedingly fine mesh 

 of minute interlaced needles of hornblende and plagioclase. 

 In general none of these last rocks have the hampshiroid habit 

 with megaphenocrysts of hornblende like those of other well 

 known localities. 



West Dike. — One of the most interesting of these varieties 

 is found in a dike on the lower west slope of Locke's Hill. 

 The dike is about 20 feet in width and cuts the gilfordal 

 camptonose (essexite) near its eastern contact as nearly as 

 could be determined. It is in the northern part of the camp- 

 tonose area, has an east and west trend, and is composed of a 

 much cracked rock cut by many joint planes. 



Megascopic. — Medium dull gray ; much whitened and 

 leached on the joint surfaces ; occasional black hornblendes as 

 phenocrysts l-3 cm long and 0'5 cm broad showing 110 and 

 010 ; thickly dotted with small phenocrysts of feldspar of 



