86 NEW YORK STATE MUSEUM 



that is, between 1200 and 1400 feet above sea level. These bogs 

 act not only as the catchment basins for drainage from the sur- 

 rounding hills but also as sources for some of the small brooks and 

 tributaries of the Hudson river drainage system. 



The more resistant rock formations of this area, such as the slates 

 and the schists, constitute the more prominent topographic features 

 like the truncated crests of folds shown in the structure of the 

 Taconic range and of the smaller hills and ridges immediately to 

 the west; while the less resistant rock formations, limestones prin- 

 cipally, are found in the larger north-south valleys. 



General Geology of Area 



As no intensive geological work has been done south of the Auster- 

 litz area in Columbia county, our knowledge of the general geological 

 relations of the manganese belt can only be inferred by correlating 

 certain type specimens with those known to exist farther north 

 along the strike, as described by T. N. Dale (4). In referring to 

 the areal distribution of the principal formations of the region, this 

 writer says that " at the north the Cambrian belt narrows and is 

 bordered on both sides by Ordovician shale and grit. Ordovician 

 schist, the metamorphic equivalent of the shale and grit, constitutes 

 the Taconic range and merges into these at the west. There are 

 also a number of very small areas of Beekmantown shale (lowest 

 Ordovician) overlying the Cambrian. Finally the Rensselaer grit, 

 with its interbedded slate and shale, representing the basal part of 

 the Silurian, constitutes the plateau, besides an outlying lenticular 

 area of 4 J square miles in Nassau and Chatham, another of half a 

 square mile near North Nassau, and a much smaller area resting in 

 the Ordovician schist near Spencer town in Austerlitz, 12 miles south 

 of the plateau." 



In a further contribution (5:297) the same writer expresses the 

 view that the mica schist referred to is the Berkshire schist of the 

 Ordovician system, whereas the grit found in the vicinity of Canaan 

 and Spencertown is probably the Rensselaer grit of the lower 

 Silurian, as these rocks not only appear to be the same so far as 

 microscopic characters are concerned but are on the strike of the 

 mapped occurrences to the north and bear somewhat similar strati- 

 graphical relations to each other, the grit overlying the schist. In 

 the vicinity of Canaan, at the Girdler road corners, gently southeast- 

 dipping purple and green slates were found interbedded with green 

 Rensselaer grit, the latter occurring with cavernous quartz veins 



