7

Mapping the Land

Geologic mapping is, in many ways, just a scientific version of "connect-the-dots . " Because of forests, soil, lakes, and cities (what many a frustrated bedrock geologist has been heard to refer to as "the damn overburden"), the underlying rock only occasionally peeks a nose out of the ground. The geologist excitedly walks up to this nose, whacks at it with a rock hammer, and dutifully marks the spot and rock type on a map. When a large number of these spots have been recorded on the map, the geologist draws the best picture possible from the limited information. Unfortunately, the dots on a geologist's field map are never conveniently numbered in sequence as with a child's connect-the-dots game, and many possible pictures can often be drawn with the same dots. This is where interpretation (which is really more art than science) and controversy come in.

Actually, in modern geologic mapping, things are not quite as bad as the description above implies. There are now many tools for investigating the rocks that lie below the surface and between the dots, testing the accuracy of a geologist's interpretations. One of these methods is to drill deep bore holes into the ground to sample what lies below; another is surveying the Earth's magnetic, gravitational, and acoustical properties - what is called geophysical mapping. But for the early mappers, it really was a game of connect-the-dots.

The first map showing Connecticut's geology was published by William McClure in 1809.¹ McClure's map showed the entire area of

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