Page:The Journal of geology (IA journalofgeology21894univers).pdf/45

to me for examination by Professor Eugene Smith of Alabama, proved to contain nothing which could be identified as ancient volcanic material.

The above rapid survey of the now known and probable areas of ancient volcanic rocks in the crystalline portion of the Appalachian system reveals the fact that this class of material is both abundant and widely distributed. From Newfoundland to Georgia it has been identified. For many areas the evidence of surface or volcanic origin is conclusive, while in many others it is as yet only probable.

The areas of these ancient volcanic rocks now known fall roughly in two parallel belts (see map); of these the eastern embraces the exposures of Newfoundland, Cape Breton, Nova Scotia, the Bay of Fundy, Coast of Maine, Boston basin and the central Carolinas; while the western belt crosses the Eastern Townships and follows the Blue Ridge through southern Pennsylvania, Maryland, Virginia, North Carolina to Georgia.

The purpose of the present communication will be accomplished if it succeeds in directing attention to this group of rocks. New areas should be added; probable areas investigated; and known areas monographed all along this old mountain range. How fruitful a field is here spread out to students of geology and petrography may be seen from the results of work in analogous regions by Harker^[1] and Mügge.^[2]

The identification of truly volcanic rocks in highly or partly crystalline terrains possesses far more than a petrographical significance, since by fixing what was the surface at the time of their formation, they furnish a certain datum for tracing out the sequence of later geographic changes and geological development.