164 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



crystals of brown ankerite, which are usually in grains a fraction of an inch 

 across, but at times are perfect rhombohedi-a, more than an inch in size. 



The quartzose, pale-green muscovite or sericite-schist, common in the 

 formation below, appears here also, but it is usually spotted, especially 

 on the cleavage faces, with groups of long blades of black hornblende, often 

 6 inches in length, which are radiated on the foliation faces of the schist 

 from a central area, after the fashion of a sheaf of wheat, from which circum- 

 stance President Hitchcock named the mineral fasciculite. Although the 

 name has passed into the list of synonyms, I have found it useful as a desig- 

 nation of the sericite- and chlorite-schists in which these hornblende blades, 

 often in sheafs, appear as quasiporphyritic inclusions which have the habit 

 of a somewhat constant accessory, rather than of an essential constituent, 

 of the rock in question. There are thus fasciculite-chlorite-schists and 

 fasciculite-sericite-schists; but this very generally disseminated hornblende 

 has been ignored in mapping, and the large amphibolite beds which are 

 represented on the map are black, purely hornblendic schist.s, free from 

 any \'isible micaceous mineral. This general distribution of hornblende 

 distinguishes the Hawley formation or series from the beds which precede 

 and follow it, wherein, outside of the amphibolite beds, hornblende is very 

 rare and for the most part wanting altogether. None of the hornblendic 

 bands in this series show any tendency to serpentinization. 



DISTRIBUTION. 



The band enters from the southwest corner of Halifax, "N^ermont, with a 

 width of a mile, and begins at the Davis mine to widen, crossing the Deerfield 

 River with a Avidth of 3 miles. It goes across Hawley with this width, and 

 is bounded on the west by a great fault. As it enters Plaintield the Goshen 

 schists begin to overlap it rapidly, and it crosses this town, Cummington, 

 and Worthington with a width of half a mile. As it enters Chester a second 

 overlap of the Goshen schist cuts it off entirely. Farther south no series 

 possessing its lithological peculiarities and richness in iron can be found. 



DETAILED DESCRIPTION. 



The whole eastern slope of the deep valley that separates Middlefield 

 and Worthington is underlain by the rocks of this series, and the large 

 garnets, superficially changed to chlorite, and the slabs of fasciculite furnish 

 many attractive specimens for the cabinet. 



