24 THE JOURNAL OF GEOLOGY. 



canic ashes, most of them composed of very sharply angular 

 fragments of devitrified glass or pumice with beautiful flow 

 structures. The delicate detail produced by trichites in one of 

 these is rather roughly represented in Fig. i. It is not unlike 

 the devitrified glass-breccia described by the writer from Onap- 

 ing river in the Sudbury district.^ 



The specimens collected by Mr. Mathews at Mount Kineo 

 on Moosehead Lake, and kindly loaned me for examination, are 

 typical quartz-porphyries or keratophyres, some of which exhibit 

 such perfect and delicate flow-lines that they can be regarded 

 only as devitrified glassy lavas. 



In New Hampshire felsites and quartz-porphyries abound. 

 They were regarded as eruptive by Hitchcock and by Hawes 

 when they occur in dykes, although the latter regarded many of 

 them, especially when interstratified, as sediments fused in sitii.'^ 

 There are as yet no published descriptions which make it reason- 

 ably certain that truly volcanic, as contrasted with abyssal 

 igneous rocks, occur within this state. 



The important development of ancient volcanic rocks in 

 eastern Massachusetts, in the neighborhood of Boston, has been 

 more discussed than any other similar region on this continent. 

 An excellent resume of the development of opinion regarding 

 these rocks has been given by Whitney and Wadsworth.3 E. 

 Hitchcock held correct views as to the igneous character of all 

 the massive rocks, although he regarded the amygdaloids and 

 some of the apparently stratified felsites as altered sediments. 

 Later the influence of Hunt created a general impression that the 

 greater part of these rocks — even the granites — were of sedi- 

 mentary origin. Wadsworth was the first to successfully combat 

 this idea, and to show that not only were the coarsest massive 

 rocks igneous masses, but even the finer jaspery felsites and their 



'Bull. Geol. Soc. Am., Vol. 2, p. 138, 1891. 

 Report of the Geol. Survey of Canada, 1890-91, F. p. 75. 



^ See Geology of New Hampshire, Vol. 2, p. 260, and Vol. 3, part IV., Mineralogy 

 and Lithology, p. 171, 1878. 



3 The Azoic System, pp. 398-44C, 1884. 



