THE NEWER CORES AND SHORT DIKES. 481 



with black dust, occupies the interstices. Large, fresh, porphyritic augites 

 appear, which are ofteu twinned ; and small, very brightly polarizing grains 

 seem to be olivine. 



THE NEWER SERIES OF CORES AXD SHORT DIKES. 



BELCHERTOWN. 

 THE FIRST VOLCANIC CORE. 



This is situated about loO rods southeast of the east end of the Holyoke 

 main sheet of trap and 2,100 feet N. 47° E. of the house of H. Moody, on 

 the Bay road in Belchertown. It is just south of the source of a brook and 

 within the edge of the woods, rising in a small knoll. On the north edge the 

 contact with the sandstone is well seen, and the baking of the latter is 

 unusually severe. The alteration has hardly l^eguii to decrease in the width 

 exposed — above 10 feet. The coarse red sandstone is baked into a hard, 

 light-gray graywacke, its mica and feldspar grains having been so affected 

 by the heat that they have been removed by later infiltration, leaving pores 

 coated with rust. Still nearer the contact the sandstone contains many white 

 compact masses, which are in part hollow tubes and seem to be bones of a 

 reptile of about the same size as that found in the sandstone at Springfield. 

 The rock is here rendered hard and impervious, and this has favored the 

 preservation of the bones. The specimens contain lime phosphate. 



The trap is fresh, very fine-grained, and shows few steam pores. Very 

 thin, well-formed plagioclase crystals, flattened parallel to c» P q6 , and of 

 the earlier and larger generation, are visible with the lens. 



THE SECOND CORE. 



The second of the series of old craters or volcanic throats is exposed 

 in a row of low knolls in the field opposite the house of J. A. Barrett, 

 where the Bay road has just crossed the mountain toward Belchertown 

 village and near the western line of the same township. The exposure is 

 only about 15 rods long by 3 rods wide, with strike N. 60° E., and near at 

 hand on all sides are abundant outcrops of conglomerate, which proves it 

 to be an isolated deposit of limited extent. It agrees in all essentials with 

 the rock of the newer intrusive dikes. 



MON XXIX 31 



