456 GEOLOGY OF OLD HAMPSHIRE C017:iirTY, MASS. 



The above description applies to all contacts from the east end of the 

 bed to the Connecticut River and from the W estfield River to the south line 

 of the State. 



CONTACTS OF SANDSTONE ON DIABASE WHICH IS KNEADED FULL OF LIMESTONE 



AND SHALE. 



Between the Coimecticut and Westfield rivers fine shales rest on the 

 trap, and the upper surface of the latter is full of inclusions of limestone and 

 shale. This can be seen just south of the station of the Mount Tom Electric 

 Road, but it can be studied best at Dibbles Crossing on the south line of 

 Holyoke, as described below. 



SECTION OF TRAP FILLED WITH LIMESTONE FRAGMENTS ON THE WESTFIELD- 

 HOLYOKE RAILROAD. 



At the first rock cuttings in the main trap sheet on the raih-oad near the 

 south line of the town of Holyoke the upper surface of the bed is exposed 

 and is covered by thin-fissile argillaceous sandstones containing Pachy- 

 phyllum. For a distance on the strike (north-south) of 1,475 feet, and 

 with the dip (east-west) of 200 feet, the upper portion of the bed, to a 

 thickness of 6 to 12 feet, is so filled with fragments of the clayey limestone 

 and sandstone that everywhere the two rocks are present in about equal 

 quantity. The limestone is in small pieces, angular and little altered, or the 

 pearl-gray fragments are molded and kneaded together with the trap. It is 

 as if the trap, plastic from heat, were molded together with the marl, plastic 

 from moisture. The trap is fine-amyg-daloidal, the cavities filled with 

 secondary calcite and diabantite. In the section figured on PI. Ill, fig. 4 

 (p. 208), the trap is already solid; the mud flows into its minute cavities. 

 When polished suriaces of the mass and thin sections are examined, the 

 fact of the mutual molding of the two rocks is clearly established. (See 

 PI. VIII 6, figs. 1,2, p. 428.) 



With a lens the limestone is seen to be fine-oolitic, at times very dis- 

 tinctly so, with round grains 0.6 to 0.9°"" in diameter and made up of finely 

 granular material dusted with minute opaque grains. There is only rarely 

 a trace of concentric structure. At times the amount of clay becomes con- 

 siderable and the fragments are of a thin-laminated calcareous marlite. 

 That this limestone was deposited in place and has molded the trap is 



