Page:The Journal of geology (IA journalofgeology21894univers).pdf/28

It is the purpose of the writer in the present paper to maintain that in the great crystalline belt of eastern North America, large areas of volcanic rocks occur, and that these, in spite of their great age, are in all respects the same as modern volcanic materials, save for alterations subsequent to their original formation among which alterations devitrification has been one of the most important.^[1]

I shall now proceed to summarize the present state of our knowledge of these volcanic areas, as far as they belong to the Eastern or Appalachian crystalline belt, omitting all reference to the central Canadian, Lake Superior, Missouri, or other more western regions of similar nature. In this review I shall commence with Newfoundland and follow them southwest, parallel to the coast.

Eastern Canada.—In a recent comparison between the Eozoic and Paleozoic rocks of eastern America and western Europe, Sir William Dawson says that the Huronian was evidently a coarse marginal deposit, accompanied by abundant volcanic outbreaks, similar to those which occurred about the same time in Wales. He is also confident that many of the bedded Huronian rocks are really of volcanic origin, being ashes in an altered state.^[2] In the same paper he mentions volcanic rocks, both lavas and pyroclastics, as abundant in the Ordivician and Silurian formations of eastern Canada.

The reports of the Canadian and Newfoundland surveys abound in references to rocks of a volcanic character in the early Paleozoic and pre-Paleozoic horizons. These references are, however, always purely those of a field-geologist engaged in a rapid reconnaissance. The frequent use of such field terms as felsite, porphyry, trap, amygdaloid, agglomerate, breccia and ash suggest a vast development of contemporaneous volcanic