2 2 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [BulL 



development of a greater amount of muscovite, almost complete 

 absence of biotite, and the restriction of the quartz to a few layers. 

 One hundred and two hundred feet beyond here there occur a 

 fifteen-foot and a forty-foot bed of grayish white quartzite with 

 very little banding. This is composed of eighty per cent quartz 

 in grains with rather plain edges and mosaic texture, fifteen per 

 cent clinozoisite, a little magnetite and colorless amphibole. 



This is followed by a series of garnet, hornblende and sericite 

 schists about one hundred and fift}^ feet thick. The first is a 

 coarsely crystalline, massive mixture of andesine, quartz, stauro- 

 lite, unorientated muscovite and biotite, and rare garnets. Certain 

 layers in this rock are composed of large, well-crystallized garnets 

 containing inclusions of quartz and magnetite and altering to 

 chlorite and some epidote. These are set in a ground mass of 

 plagioclase, quartz and chloritized mica. Next follows a thirty- 

 foot bed. of dark green hornblende schist speckled with pink garnet 

 crystals a few millimeters in diameter. This rock is composed 

 practically entirely of a fibrous green hornblende in short irregular 

 laths and in aggregates of many crystals, and quartz. Rare grains 

 of apatite and a little magnetite and plagioclase are seen through- 

 out. The small equidimensional garnets cut irregularly across the 

 foliation. This is followed by a twenty-foot bed of dark green 

 hornblende schist without any garnets and with a greater propor- 

 tion of iron oxide. The last of this series is a muscovite schist 

 full of pinkish garnets and lesser amounts of titanite that give it 

 a rough gneissoid apoearance. 



The next few hundred feet of the tunnel contain a few more 

 bands of white muscovite schist from five to ten feet thick fol- 

 lowed by two thousand feet of quartz and mica schist exactly like 

 the first part. From there to a point within five hundred feet of 

 the eastern corner in the tunnel the rock alternates between a dark 

 green, fine-grained hornblende or hornblende mica schist and a 

 sandy mica schist (Plate v b). From there to the contact between 

 the Hartland and the Brookfield diorite, one hundred ninety-five 

 feet northwest of the corner, the schist returns to its normal alter- 

 nation of quartz and mica types. These persist right up to the 

 contact where considerable black tourmaline, garnet, and staurolite 

 are developed in the otherwise normal mica schist. The tourma- 

 line alone of these minerals is not to be found in many parts of 

 the rock and may represent additions from the diorite magma 

 intruded into the schist. 



STRUCTURE 



Throughout the length of the Hartland section exposed in the 

 tunnel, the dip is invariably to the west and the strike east ot 

 north. Readings on the dip show a gradual increase from twenty- 

 five degrees west at the contact to fifty-four degrees west at the 

 portal with no great variation at any one point. The strike veers. 



