Page:The Journal of geology (IA journalofgeology21894univers).pdf/424

Cambrian conglomerate gneiss resting unconformably upon the upturned edges of a coarse gneiss associated with coarsely-crystalline limestone (Emerson's Hinsdale limestone). A line of Algonkian rocks extends southward from Hoosac Mountain (including the Stamford gneiss forming the core of the mountain) in a belt of oval areas across the Berkshire County Plateau. On lithological grounds these rocks would be correlated with some members of the Mount Holly series of Vermont to be described below. They may, however, be equivalent to the upper series of the Algonkian which has suffered less metamorphism to the north. The lack of fossil remains in the lower series cannot be used as evidence, since metamorphism has probably obliterated all traces of them. A disparity between induced structures in the two belts is also of no value as the quartzite has not recorded the regional cleavage owing to its massive character. Rocks stratigraphically above it, however, may have had the cleavage developed. The evidence against this delimitation is furnished by the apparently conformable mica schist, which, as a rule, accompanies the quartzite, and more locally other members of the series as well, which may have contained the Olenellus fauna. It must be left for future work to determine beyond dispute the relations of the series immediately below the Olenellus zone to the quartzite, whether the rocks are conformable or unconformable; if the former, whether the delimitation of the Lower Cambrian shall be placed above the mica schist or below it. Tentatively, the series just below the quartzite, the mica schist at the top and the conglomerate at the bottom, will be considered wholly or in part of Algonkian age. The separate numbers of this series with estimated thicknesses will now be described.

As far as known the best section of these rocks occurs in the town of Mendon, one mile north of Mendon village, on the west slope of Blue Ridge Mountain (Rutland Sheet). All the members identified occur here, although no single section thus