268 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



continuous and undisturbed tliat it is impossible to think of faulting or 

 any irregularity at the junction any more than at the opening fiirther 

 south under the birches, where the junction is equally undisturbed. The 

 paleontological evidence reenforces the stratigraphical for the continuity 

 of the limestone and the quartzite. At its northern end, overhanging 

 the brook in the most northerly digging, the magnetite layer is a black 

 magnetite-pyrite-chlorite rock. (Fig 18, and e, fig. 15). This rock which 

 caps the limestone contains amphibole, biotite, chlorite, a little pyi'ite, 

 magnetite, and hematite, and an amorphous mineral resembling serpentine. 

 The biotite is very dark-colored in basal sections, and in places changes into 

 chlorite and passes at the edges into the serpentine-like mineral. In the 

 larger part of the section the latter has a fibrous stmcture, with the fibers, 

 grouped into large, elongate patches, at times radiate, and the whole 

 resembles a fine hornblende-schist. It is of oil-green color, shows only in 

 patches a trace of dichroism, and with polarized light there is a faint 

 predominance of extinction at about 3° from the long axis of the fibrous 

 groups, which proceeds from the whole group; and this is overlain, as it 

 were, by the aggregate polarization of the fine scales and needles of the 

 sei-}3entine-like mineral. An analysis made for me by Mr. Gr. H. Corey, of 

 the class of '88 in Amherst College, gave: SiO^, 42.56; FeA, 44.25; CaO, 

 13.11^99.92. The absence of magnesia from this analysis is jjuzzling, as 

 the product of decomposition of the hornblende resembles serpentine 

 strongly. It is possible that a highly ferruginous amphibole has developed 

 in the mag-netite-calcite bed, and that this has changed into a ferruginous 

 mineral allied to chloropal. 



TJie eastern bed of quartzite (5). — Under the birches, as presented in the 

 section (fig. 17), 34feet of a thin, evenly laminated, light-gTay quartz-schist 

 caps the limestone and is very rusty, especially at the base, and porous from 

 the amount of jiyrite and calcite that has been removed. Two-thirds the 

 way up a layer of about 4 inches thickness is crowded with flattened and 

 distorted casts of bracliio})ods and of annulate crinoid stems. A large spirifer 

 with septa like S. disjimcta is very abundant. Traces also of Rh3^nchonella 

 and Orthis are common, of Nucula and Platyostoma rare, and the ringed 

 crinoid stems are again very common. The fossiliferous part of the bed is 

 of very limited lateral extent, and I could trace it onl}- about 10 feet. 



The next outcrop, 150 feet east and about 6 feet above the bed just 

 described, is a hard, gray, quartzose conglomerate, witli white, flattened quartz 



