Page:The Journal of geology (IA journalofgeology21894univers).pdf/38

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. 1. It is not unlike the devitrified glass-breccia described by the writer from Onaping river in the Sudbury district.^[1]

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 situ.^[2] There are as yet no published descriptions which make it reasonably 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 résumé 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 sedimentary 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