No. 40] GEOLOGY OF SHEPAUG TUNNEL 3 1 



parts have no peripheral or other regular arrangement nor are 

 they always marked off sharply from types with a granitic texture. 

 The varying degree of foliation represented shows that these 

 various parts were intruded at slightly different dates, ranging 

 from before the end of the regional pressure till after the cessation 

 of all metamorphism. 



The biotite-hornblendite dikes, like their supposed relatives on 

 Mount Prospect, are unmetamorphosed. They were intruded late 

 in the sequence and nearly always occur within a schistose area of 

 diorite or between a schistose and a massive type. 



The Schist Inclusions in the Diorite 



The diorite contains a considerable number of inclusions of 

 quartz and mica schist, mostly too small to be mapped on the scale 

 employed, clearly related to the Hartland schist. These are most 

 plentiful near the central part of the diorite and disappear entirely 

 within a few thousand feet of the Brookfield-Berkshire contact 

 on the west. As was mentioned before, the strike and dip of these 

 included layers varies with that of the foliation in the diorite. 



The mineralogy of these inclusions is much the same as that of 

 the rest of the Hartland series. Quartz, biotite, muscovite, some 

 plagioclase, garnet, apatite, and pyrite are the common minerals. 

 Rare titanite, sillimanite, calcite, and in some cases considerable 

 diopside are the additional minerals not found in other parts of 

 the schist. These bands represent the quartz and mica schist f acies 

 of the Hartland only slightly changed chemically but with very 

 different textures. In place of the simple recrystallization tex- 

 tures seen before, we find cataclastic textures with a true mortar 

 texture in some cases (Plate viii a) . In these the quartz is crushed 

 around large and slightly strained feldspars, the biotite is bent 

 around these more resistant masses and much sillimanite is formed 

 in curved rods or bundles. In certain cases a good deal of graniti- 

 zation of the inclusion had taken place before it was incorporated 

 into the diorite and bands of quartz and orthoclase with a little 

 micropegmatite alternate with quartz, biotite and sillimanite f oliae. 

 Both of the bands show crushing. In one instance the schist 

 inclusion is directly alongside a dike of rather gneissoid Thomaston 

 granite and itself contains an unusual amount of quartz and some 

 fresh microcline grains. 



The calcite that is found in most of these schists as well as in 

 the diorite itself is very rarely if ever formed in place from the 

 alteration of the plagioclase but is usually introduced along micro- 

 scopic veins and faults. Only one case is known where the calcite 

 is present in appreciable quantity as small irregular grains through- 

 out the rock and that is in the quartz diopside schist at the entrance 

 to the tunnel just west of the Bantam River crossing. Pyroxene 

 forms ten per cent or more of this rock and quartz eighty to 



