When man first settled the United States, two natural features favored settlement; flat land that was easy to build on and to farm, and a nearby river that could act as a source of water, transportation, and power. The Connecticut River Valley from Middletown, Ct. north past the Connecticut-Massachusetts state line satisfied these two needs, and was favored by many early Americans in New England. This area remains an area of rapid urbanization, partly because of the broad flat lowlands.

The subdued topography of this area is due in large part to deposition of fine-grained materials into glacial Lake Hitchcock. This lake was formed during the Wisconsinan age when southward drainage in the Triassic valley of Connecticut was dammed by glacial drift in the area of Rocky Hill, Connecticut. Lake Hitchcock grew to and beyond St. Johnsbury, Vt. with much of the lake being filled with cyclical lake-bottom deposits during the 2,290 to 2,350 years of its life.

Aside from the relative flatness inherent in the deposition of fine-grained lake-bottom deposits, these deposits present very few characteristics that are favorable for urbanization. Favorable characteristics are possible sources of clay for manufacturing and possible sources for waste storage sites. Unfavorable characteristics include low water yields resulting in poor urban water-supply sources, and very low flows in streams during dry periods; low percolation rates resulting In drainage and septic problems; and low or uneven bearing strength which create problems in construction. 

Fine-grained lake-bottom deposits have been mapped for six quadrangles in the Connecticut Valley lowlands; the quadrangles of Windsor Locks, Broad Brook, Hartford North, Manchester, Hartford South, and Glastonbury (all located in Connecticut). All the maps were prepared from existing information including well and test hole data on file at the Water Resources Division in Hartford, surficial geologic quadrangle maps, and bedrock contour maps. The maps also reflect geologic interpretations of the history of glacial Lake Hitchcock.

The Hartford North maps were prepared as test maps to determine if the project was feasible. They were prepared using the previously described information plus additional subsurface data obtained from engineering firms and the State Highway Department.

During preparation of the maps, an arcuate-shaped, ice-contact deposit composed of coarse sand and gravel was delineated in the Broad Brook and Windsor Locks quadrangles. This feature marks the location of a zone of stagnant ice In front of and marginal to active ice to the north.

Two types of maps were prepared for the area in study; Thickness of the Principal Clay Deposit, and Thickness of Material Overlying the Principal Clay Deposit. The term "principal clay deposit" refers to the fine-grained lake-bottom deposits of Glacial Lake Hitchcock. These maps define the distribution of the deposit, and show the thickness of the deposit in 50 foot intervals and the thickness of the material overlying the deposit In 20 foot intervals. The maps indicate that much of the area is underlain with substantial thicknesses of finegrained lake-bottom deposits (50 feet thick or greater), and that much of the deposit is within 20 feet of the surface.

The maps included in this report can be used for land-use planning. Uses include location of favorable sites for specific uses such as landfills, utility corridors, heavy construction, etc; location of problem areas for specific land uses; identification of possible problems for specific areas; design and construction cost estimates; and prospecting for exploitable clay deposits. It Is suggested that, for effective planning, these maps be used together or in conjunction with other maps such as maps showing surface materials, depth to bedrock, depth to water table, and flood prone areas.