490 NEW YORK STATE MUSEUM 



At Roe's spar bed, one mile south of Towner pond, three diabase 

 dikes cut the huge pegmatite exposure. One occurs near Fleming 

 pond, one mile south of Hammondville ; another in the gneiss a mile 

 northwest of Penfield pond. 



Acid dikes of the type known as Bostonite were found in two 

 localities : one at Heart pond, the other north of Worcester pond. 

 These dikes are bright red and are very small. 



Palaeozoic formations. Potsdam sandstone. As shown on the 

 map, the Potsdam occurs in three localities. Of these the Chilson 

 area is the most important. There are three good outcrops in this 

 area. On the hill near the gabbro are ledges of yellowish quartzite, 

 and not far away in the fields are several small outcrops of con- 

 glomerate. The conglomerate and .reddish sandstone represent the 

 basal Potsdam. Farther east in the brook is an exposure showing 

 the contact with gneiss. This also is the reddish lower facies. To 

 the south on the road to Putnam pond is an outcrop of a gray color, 

 which represents the upper facies and is slightly calcareous, showing 

 a gradation towards the Calciferous. 



These exposures all rest unconformably upon the quartzose gneiss, 

 and the conglomerate contains pebbles of the same gneiss. 



The Crown Point area of Potsdam sandstone is a small remnant 

 of the reddish yellow type. It has the usual strike of n. lo e. and 

 dip of ID n. w. A pretty little postglacial canyon, with some 

 cascades, is to be seen where the north branch of Putnam creek 

 crosses this Potsdam area. Many loose boulders of Potsdam sand^ 

 stone and of Calciferous, Chazv and Trenton are scattered about 

 the fields near this locality. These rocks are not glaciated but indi- 

 cate the former presence of these formations in the valleys. 



The exposure on Trout brook shows interesting cutting of the 

 stream channel laterally down the dip, with resulting cliffs on the 

 down-dip side. The rock is the reddish variety, with a strike of 

 n. 20 e. and a dip of 15 n. w. 



Trenton limestone. In a cut of the abandoned railroad, about a 

 mile west of Ironville, are a series of small exposures of dark gray 

 limestone, containing typical Trenton fossils. A steep and very 

 variable dip, with some variation in strike, points to the possibility 



