No. 40] GEOLOGY OF SHEPAUG TUNNEL 23 



from north forty-five degrees east near the diorite, where it 

 appears to parallel the contact, to a maximum of north seventy- 

 five degrees east just west of the central portion and then swings 

 irregularly back to north two degrees east at the portal. A short 

 tunnel, 1635 feet long, drilled under the southern extension of 

 Guernsey Hill one half a mile east of the outfall of the seven-mile 

 tunnel (see map facing page 16), exposes a section with the 

 dip averaging forty-five degrees west but with a strike of north 

 ten deg^rees west. The rock here exposed is a repetition of quartz 

 and mica schist. 



Outcrops of the Hartland schist are rare in the area mapped. 

 In the hills east and northeast of Litchfield village there are a good 

 many surface exposures of coarsely crystalline garnetiferous mica 

 schist with a north-south strike and a dip west of vertical, while 

 south and southeast of Bantam Lake there are a number of out- 

 crops of fine-grained mica and quartz schist that strike from north 

 seventy to north eighty east and dip northwest. At the southwest 

 corner of the area near Mount Rat the Hartland — a lustrous, some- 

 what sandy, fine-grained mica schist — forms a number of irregular 

 re-entrants into an intruded mass of hornblende gneiss. The 

 strike is nearly east-west and the dip north. 



It can be seen from this that the surface exposures give no more 

 idea of the amount of folding that may have taken place than does 

 the underground section. Either the beds compose one thick series 

 all tilted one way or a series of overturned folds with isoclinal dip 

 planed oflf by erosion and intersected by the tunnel far from the 

 ends of the folds so that the dip of the original strata and the 

 schistosity coincide. If the first be true, a series of immense thick- 

 ness is present, more than eight thousand feet for the tunnel sec- 

 tion alone, and that is but a small part of the whole. In consider- 

 ing the second case it is true that any amount of repetition could 

 be present in the main tunnel and in the short east section without 

 changing the endless sequence of quartz and mica schist inter- 

 sected by dikes of pegmatite. A consideration of the great thick- 

 ness required by the first assumption is in itself enough to make 

 repetition by folding almost a certainty. The amount of such 

 repetition cannot be determined but we can at least assign a 

 minimum thickness to the series. The sequence of sericite, horn- 

 blende and garnet schists described previously and located near 

 the central part of the main tunnel represents an easily recognized 

 sequence which assuredly is not repeated in a linear distance of a 

 little under two miles. With an average dip of forty degrees the 

 thickness of the formation in this distance is 6500 feet, and if the 

 telltale series were to come in immediately beyond the exposed 

 area, the thickness of the formation without repetition of this 

 series would be 3250 feet. 



