1906.] GEOLOGY IN RELATION TO WATER SUPPLY. 295 



ply. Rocks of this character are, however, oftentimes filled 

 with joints and cracks which are not due to the original tex- 

 ture of the rock, but to the movements of the earth's crust 

 which have taken place since the rock was formed. Under 

 such circumstances crystalline rocks — granites, gneisses, and 

 schists — contain a large amount of water, but it is not evenly 

 distributed, and it is a chance that a particular well will be 

 sunk in such a way as to take in the water occupying the 

 crevices. Reports have come to me from places in this State 

 where wells have been completely abandoned or used only dur- 

 ing rainy seasons because they have been sunk in un jointed 

 crystalline rocks. It is such rock that forms the beds of the 

 upper tributaries of the Connecticut, and which enables that 

 river to receive such a large share of the water which falls as 

 rain. 



The bed rock of the Connecticut Valley district, reaching 

 from New Haven to Thompsonville, and extending from Mix- 

 ville, Bristol, and North Granby on the west to Middletown, 

 Glastonbury, and Hazardville on the east, is a sandstone of 

 various grades of fineness, from clay-shales to conglomerates 

 containing pebbles two or three feet in diameter. These rocks 

 are made of grains more or less closely cemented together 

 with iron, clay, and lime. There is considerable space about 

 these grains, which may be occupied by water and, as a rule, 

 each grain i.s surrounded by a film of water. Such rocks, 

 therefore, are very favorable for water-bearing beds and may 

 contain as much as 30 per cent, of their volume. Wells sunk 

 in the sandstone in Connecticut yield abundantly, are rarely 

 abandoned, and rarely do they need to be dug to great depths. 

 In the list of wells in Connecticut, published in Bulletin No. 

 102, U. S. Geological Survey, it will be seen that a great num- 

 ber of the strongest flowing and most satisfactory wells and 

 springs of the State are located in the sandstone belt. 



The surface covering of rock in Connecticut is almost en- ■ 

 tirely of glacial origin. The soil formed during thousands of 

 years of exposure to the atmosphere and water has been re- 

 moved and carried to the south. If a hilltop in Connecticut is 

 compared with one south of the glacial line a great difference 

 will be noted. The southern peak shows rock fragments in 

 all stages of decay, which have weathered from the mass un- 

 derneath. They are part of the bed rock and have been de- 



