The influence of erosion on the landscape. Erosion has been so deep that there is little, if any, relationship between the individual hills and valleys of 250 million years ago and those of today.

The whole bewildering mess of rocks in Connecticut may be reduced to just these four divisions. Geologists will sometimes subdivide things even further, but these four form the basics. These are the rocks Percival spent seven continuous years mapping. And these are the rocks that have been studied since by hundreds of geologists, sometimes mapping almost as much detail in a few square miles as Percival described for the whole state. But it was necessary to have this incredibly detailed knowledge to get to the point where we could distill out the most important divisions. From the over one hundred different rock formations shown on the newest state geologic map, we can now confidently reduce everything to the fundamental foursome.

The close control of landscapes by terranes should not lead one to believe Connecticut's landscapes have changed little since the collision and break-up. Erosion has been the land's steadiest habit since Pangaea split apart. At one time, the rocks at today's surface were more than five miles underground: the persistent nibbling of the land by erosion has removed at least that much. The upper layers now removed by erosion could have been very different from what we see at the surface today, and thus the landscapes would have differed as well. Yet the outlines of today's terranes probably bear close resemblance to those of earlier times.

Battered cars rusting in a junk yard illustrate the relationship between landscape and terrane. The situation in Connecticut today is as if erosion has rusted away each terrane down to the chassis. The exterior bodies of the terranes - the sheet-metal hills and ridges of the original landscape - have long since crumbled, but each chassis still retains the terrane's general outline. Thus, the main landscape divisions have not changed significantly, but the form of the land surface - the shape and location of its individual hills and valleys -is almost completely different.

But despite the great depth of erosion, every feature of Connecticut's landscape is, in some way, related to terranes. For example, trace the plight of the poor Uplands farmer cursing the land for growing more stones than corn. The stones are in the soil because of glaciation. Glaciation put them there because the Uplands metamorphic rock makes for tough old beans that resist the glacial grinding machine. And

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