From the north boundary of the Park and along the Lake Champlain shoreline older and older Ordovician rocks are _encountered_.[22] The rocks (see geologic map, Fig. 11), primarily tilted marine limestones, display a variety of fossils, some of which are illustrated in Plate 1. Figure 12 is a view of the west side of Button Island showing an 18-inch thick reefy zone in the Orwell limestone. The reefy zone is composed largely of tumbled heads of colonial corals and stromatoporoids. A selected list of reference books and articles, some of which contain plates picturing Ordovician fossils, is found at the end of this section. Ordovician and older rocks were lifted, folded and faulted during the Taconic Disturbance. Dramatic evidence for this period of crustal instability is seen in the Champlain Thrust, a major series of faults which can be seen east of Button Bay State Park. The evidence for such a fault system, which is more fully discussed in another pamphlet, is readily seen on Mount Philo where older Cambrian rocks have overridden (been thrust over) younger Ordovician ones. As time passed in the Button Bay region younger and younger sediments were deposited over the top of folded and eroded Ordovician rocks. These sediments became rock and in turn slowly broke into fragments which were transported to other areas where they were deposited again as sediments. The glaciers passed over, leaving their rock debris behind as they wasted northward. Marine clays were slowly deposited from the waters of the Champlain Sea. Today only the marine clays resting on the beveled edges of Middle Ordovician rocks can be seen in the Park. The history of the earth is open for all to read. Button Bay State Park can tell us only the history which is recorded in its clays and underlying rocks. As we have seen, there are certain giant geologic time gaps in the Park area, but many of these do not exist in other places and in other Parks. If this pamphlet has stimulated an interest in filling in these time gaps through your study of rocks in other places, then it has fulfilled its purpose. The present interest in Space demands a good long look at the Planet Earth. Good Hunting! [Illustration: Figure 12. Bedded Orwell limestone on open-lake side of Button Island, showing patches of stromatoporoids and colonial corals (white areas). Photo by C. W. Welby.] SUGGESTED READING _Historical Geology_, by Carl O. Dunbar, John Wiley & Sons, Inc., New York, 1960. Good general treatment of what the rocks can and do tell geologists about the history of the Earth. _Handbook of Paleontology for Beginners and Amateurs_, Part 1, The Fossils, by Winifred Goldring, New York State Museum Handbook 9 (obtainable from: Paleontological Research Institution, 190 Dearborn Place, Ithaca, N. Y.).