CRUSHED BAND AT HOLYOKE DAM. 



371 



At the east end of the section the red sandstone reappears for a few 

 rods, with the normal low dip to the east and no twisting of the beds 



On examining my maps I found that the State-line fault, 

 which I had located where it crossed the two trap ranges, 

 and had not been able to follow farther north l)eneath the 

 great sand ])lains of Holyoke, would cross the Connecticut 

 just at the place of the section. I have therefore prolonged 

 this fault so as to make it include the central shale of the 

 section, and consider this an area of crushing at the passage 

 of the fault. The tlu-ow of the fault does not seem to be 

 great, and it is probaljle that the shale is an upper member 

 dropped in between the sandstone beds and strongly crushed. 



The shales contain impressions of hopper-shaped salt 

 crystals, cubical cavities, variously distorted, from which salt 

 has been removed, and angular cavities 3 inches by J inch 

 in cross-section and 1 inch deep, from which some mineral, 

 probably barite, has been removed. jVIany shrinkage cracks, 

 often forming complex networks and broad stellate forms, 

 are filled with white calcite. 



At a much later time the abundant fissures, formed by 

 the crushing of the rock, were filled by a more complex 

 series of minerals. The oldest is siderite, which coats broad 

 surfaces with fine crystals often a third of an inch across, 

 ranging in color from a yellow^ish gray to a rich reddish 

 yellow, and as they have the faces R and co R 2 equally 

 developed they simulate dodecahedi-a and suggest cinnamon 

 garnets. Before the completion of their growth flat blades 

 of gypsum formed upon them, which have since been 

 removed. They were followed by a curious acicular growth 

 of barite— parallel groups of straight, doubly serrate needles 

 fomied of minute rhombic prisms (OP, ^P) just touching 

 by the acute angles and having the axis b common. These 

 are superficially inclosed in the siderite and project from it 

 in a common direction. 



The specimens are beautifully frosted by a growth of small white 

 calcites, R 3, » R, -f R, — 2 R, with rounded apex or coated by a layer of 



u 



