Shells of _pelecypods_[17] occur at two and perhaps three levels within the bank. They can be seen easily in many slumped clay bodies along the beach (see Fig. 10, in which the shells are mainly _Macoma_ and _Saxicava_). These shells once belonged to living animals whose very close relatives and identical younger generations are found living today in cold Arctic waters. Brown clays were deposited in a marine Champlain Sea. How did these marine waters get into the Champlain Valley? [Illustration: Figure 10. Close-up view showing the pelecypod (clam) shells which occur within the Brown Clays. Note small Ballpoint pen for scale. These shells tell us of the marine origin for these clays. The pelecypods here are _Saxicava_ and _Macoma_.] Remember from the previous discussion of Lake Vermont that as the Champlain ice lobe retreated into Canada, fresh water from Lake Vermont began to seep through the ice lobe into the St. Lawrence Valley. This seepage caused a gradual lowering of the Lake Vermont water-level until the lake reached a stage lower than the marine waters of the St. Lawrence Sea. Soon the sea water began to flood Lake Vermont and true marine conditions were reached. These marine waters reached as far south as Whitehall, New York, which is located near the southern end of present-day Lake Champlain. The maximum area covered by the Champlain Sea did not equal the greatest size attained by the fresh waters of Lake Vermont. For instance, the sea did not extend as far east as the Green Mountains except in the very northernmost region of Vermont. In the vicinity of Button Bay State Park these waters extended less than a mile east of Vergennes, and the towns of Middlebury, Hinesburg and Charlotte would have been entirely above water (see map, Fig. 7B). It has been postulated that marine waters extended throughout the length of the Champlain Valley and into the Hudson Valley, forming a continuous strip of marine water from the Gulf of St. Lawrence to the Atlantic Ocean at the mouth of the Hudson River. If this were true, New England would have been an island only a few years ago (geologically speaking). The weight of evidence available today does not support the prior existence of this connecting ribbon of sea water. Today Lake Champlain contains fresh water again, and the marine conditions have retreated back into the Gulf of St. Lawrence. What happened to permit a return to fresh water conditions? The lakes and lake-stages discussed are known from the presence of various shoreline features, most of which are now “high and dry.” Each lake or lake-stage has its own set of lake-level features. An interesting fact emerges from a study of any one former lake. The present elevation above sea level of delimiting lake-level features is _not_ the same throughout. To explain this more fully, the present elevation of those features formed when the Champlain Sea was at its maximum extent will be examined.