Page:The Journal of geology (IA journalofgeology21894univers).pdf/445

place or another all the eminent characteristics of a basal conglomerate.

An apology may be in order for dwelling so long upon the evidence detailed in support of the conclusion that an unconformity occurs at the base of the conglomerate, when, to many, the evidence afforded by the conglomerate alone would he considered amply sufficient; but in an area so greatly disturbed and metamorphosed as this, it seems best to enumerate all possible criteria that can be legitimately advanced tending to sustain the above conclusion.

To summarize briefly, this paper is hoped to have substantiated essentially the following facts:

1. That immediately beneath the Lower Cambrian quartzite in Vermont there is a series of more or less metamorphosed clastic rocks of no inconsiderable thickness; the upper member of this series being a dark chloritic mica schist; the lower member a highly metamorphosed conglomerate, and between these several pebbly limestones and pebbly micaceous quartzite strata. Evidence for and against an unconformity at the top of the schist is presented, but no satisfactory data are advanced to sustain either interpretation. The evidence for a time-break at the base of the conglomerate is thought to have been established, and the data in support of this conclusion are discussed in some detail. These rocks are referred to the Algonkian Period and are provisionally called the Mendon series.
2. That below the Mendon sedimentary rocks, a still older, more metamorphosed and more variable series of stratified rocks of Algonkian age occurs, together with gneisses and schists, whose origin is unknown, and abundant metamorphic equivalents of old basic igneous rocks. Many of the varieties of rocks occurring in this series are enumerated, and, together with their structure are contrasted with the rocks of the Mendon series, whose basal member, the conglomerate, delimits the series above. From their typical development in the town of Mount Holly, Vt., it is suggested that these rocks be called the Mount Holly Series.