The mere fact that there are no rocks representing these millions of years tells us that the sea had withdrawn from the area and that the previously deposited rocks were undergoing erosion during most or all of the missing rock gap (the time not represented by rocks). Information from adjacent areas, however, tells us that the Park rocks were tilted during the Taconic Disturbance which occurred during the final stages of the Ordovician Period. East of the Park, Taconic earth movements are more dramatically exhibited. The rocks are tilted even more than in the Park and are broken by faults or cracks in the earth’s crust. Some of these faults, known as thrust faults, positioned giant slabs of rock far from their original locations and placed older on top of younger rocks. Following these earth movements there occurred a long period of erosion. Many of the rock layers were stripped off and carried piece by piece by rivers to other regions. Hundreds of millions of years passed and then, less than one million years ago the great glacial ice sheets slowly advanced southward over the Park area. Pieces of hard rock frozen to the underside of the ice sheets scratched and scraped the rock surfaces leaving these scratches or striations for us to see today (near the northern end of the Park beach these striations are common on the outcropping rock). The retreating glaciers created a series of lakes in which clay, silt, sand and gravel were deposited. Today these sediments are found resting on the beveled edges of the Park rocks. Present-day Lake Champlain owes its existence to a general uplift of the earth’s surface, greater in the north than in the south, perhaps due to the removal of the heavy glacial ice sheet from the area. The greater uplift in the north dammed the Champlain valley which slowly filled with water. For a diagrammatic picture of the geologic history of D.A.R. State Park, see Figure 7. SUGGESTED READING Beerbower, J. R., 1960, _Search for the Past_, Prentice-Hall, Englewood Cliffs, N.J. Collinson, C. C., 1959, _Guide for beginning fossil hunters_, Educational Series 4, Illinois State Geological Survey, Urbana, Ill. Dunbar, C. O., 1959, _Historical geology_, John Wiley and Sons, New York. Fenton, C. L., 1937, _Life long ago_, The John Day Co., New York. Goldring, Winifred, 1931, _Handbook of paleontology for beginners and amateurs_, part 2, Handbook 9, New York State Museum, Albany, New York. —— ——, 1950, _Handbook of paleontology for beginners and amateurs_, part 1, Handbook 9, 2nd Edition, New York State Museum, Albany, New York. Moore, R. C., 1958, _Introduction to historical geology_, 2nd Edition, McGraw-Hill Book Co., New York. Shimer, H. W., 1933, _Introduction to study of fossils_, The Macmillan Co., New York. Simpson, G. G., 1953, _Life of the past_, Yale University Press, New Haven, Conn.