370 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



THE CHICOPEE SHALE, OR THE CALCAREOUS SHALE. 



All the bluffs in the city of Holyoke, especially the long railroad cut, 

 are made up of a gray shale which varies into a paper-thin red sandstone, 

 in which rarely a bed a foot thick can be quarried. It always effervesces 

 abundantly with acid; many beds are full of nodular concretions of clayey 

 limestone, and at times these coalesce, cementing thick beds of the clay 

 into water-lime. 



The rod-shaped concretions which have been called fucoids are want- 

 ing, but all the marks of frequent recession of the water, as mud-cracks, 

 raindrops, and ripple-marks, are present. The rock abounds in casts of 

 gypsum and of salt crystals. It extends from Holyoke southward, occu- 

 pying the central portion of the basin, and is bounded on either side by 

 the Longmeadow sandstone. 



The large quantity of hematite and of iron- and lime-carbonate would 

 seem to have been derived from the subjacent trap and trap-tuff. 



THE CONTINUATION OF THE STATE-LINE FAULT IN A CRUSHED BAND AT 

 HOLYOKE DAM, AND THE SECONDARY MINERALS FOUND IN THE FISSURES.' 



During the building of the new dam at Holyoke, the shales of the 

 area below the present dam were accessible for a long time, and a deep 

 trench was blasted from the foot of the dam halfway to the bridge below, 

 which exposed an exceptionally crushed, folded, and faulted band in the 

 shales (fig. 23). 



The section begins in midstream at the foot of the dam and extends 

 60 rods east toward the bridge. For 11 rods the rock is a red sandstone of 

 medium to fine grain, which runs in easy undulations and has a slight dip 

 north, or from the observer. A compact bed of different color from that of 

 the rest indicates a fault at the middle and end of this part of the section. 

 This is followed by a fine, brittle, calcareous shale — a slightly indurated 

 mud rock, at times massive, at times banded, generally dark-gray, but often 

 of a bright red ; some of the bands are a buff water-lime. This is strongly 

 folded, jointed, and contorted, and in several places one or two rods wide 

 crushed completely, so that all structure is gone, and after being thrown 

 out on the bank the rock slakes under the influence of the weather and 

 crumbles to powder in a few days. 



' For further discussion of State-liue fault, see the section "The Holyoke Sheet," p. 446. 



