408 THE JOURNAL OF GEOLOGY. 



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 cor- 

 related 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 suf- 

 fered 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 evi- 

 dence 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 members of this 

 series with estimated thicknesses will now be described. 



THE UPPER OR MENDON SERIES OF THE ALGONKIAN. 



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 



