Metamorphic Upper Devonian Rooks. 269 



by examining the quartzite ledges along the strike north and 

 south from this point and comparing them with the " upper 

 quartzite." 



d. The mica schist west of the limestone. — This rock is a dark, 

 even-bedded, muscovite schist, so fine grained as to be almost 

 indistinguishable from the even-bedded varieties of the argillite 

 below, with its glistening surface pitted here and there by 

 minute hollows from which small red dodecahedral garnets 

 have fallen out. It is abundantly marked by small bodies, 

 which appear much like minute altered chiastolites just visible 

 to the eye. The minute chiastolite-like forms prove to be 

 made up externally of bands of quite large muscovite plates, 

 each normal to the long sides of very impure biotite crystals, 

 the latter placed transversely to the bedding of the rock. 

 Under the microscope the rock shows a line, scaly, colorless 

 ground mass, dotted abundantly with coaly matter, and made 

 up mostly of muscovite plates with some apolar matter, appar- 

 ently opal. The constituents are a little larger than in the argil- 

 lite, and the coaly matter less abundant. No kaolin could be 

 detected. The much-fissured clear garnets are surrounded by 

 a black band from the repulsion of the coaly matter, within 

 which a broad decomposition band of chlorite in twisted scales 

 appears which often extends nearly to the center. They con- 

 tain large grains of quartz irregularly arranged. The biotite 

 incloses garnet, and the muscovite forms caps around the garnet, 

 and arranges itself symmetrically to the biotite, so the order of 

 crystallization is very generally garnet, biotite, muscovite. 

 The large amount of impurity in the biotite indicates that 

 when it formed the rock was more carbonaceous than at 

 present. Leucoxene occurs in yellowish white grains less 

 abundantly than in the argillite 



e. Fault between the schist and limestone, d, fig. 2. — The bed 

 last described dips under the limestone apparently, with the 

 strike K 70° E. and dip 25° to 35° E. But just opposite and 

 northwest of the largest excavation in the limestone, and under a 

 small apple tree where the schist seemed certainly to go under 

 the limestone, and where Prof. Dana and the writer dug away 

 and followed it for six -inches under the limestone, later I 

 had excavations made, having doubted the reality of the appar- 

 ent conformable superposition, because the bed of limestone 

 rested on the schist with abrupt transition and total want of 

 continuity. I found the two rocks to be faulted against each 

 other, the wall of the limestone bending under for a few inches 

 and then going down vertically, and the schists, so fiat in the 

 exposures below, were here crumpled up sharply and ground 

 into shapeless masses against the limestone. I followed the 

 fault down more than a meter without finding the bottom of 



