Horizon II: 14,000-12,000 Years Ago The Disappearing Lake Scientists were surprised to find a layer of gravel in the core at this horizon.  How could this gravel have reached the middle of the lake basin?  The best explanation is that the gravel was carried there by streams that flowed into the basin -- and that the lake at that time was dry.  Why did the lake disappear?  And how did it come back?  Scientists looked to the receding glacier for the answer. 1. Drained Lake Why did the lake disappear?  It was probably too chilly for it to evaporate, so scientists belive that the sediment that had built up and acted as a dam at the north end probably eroded, allowing most of the lake to drain away. 2. Grasses and sedges Pollen grains in the core from tundra grasses and other grass-like herbs known as sedges reveal that these were some of the early ground-cover plants. 3. Heaths in flower Flowering heaths were part of the upland vegetation, as indicated by macrofossil evidence. 4. Spruces and pines Spruce and pine pollen in the core points to the presence of those trees, probably growing in patches around the basin. 5. Mastodon This open spruce parkland environment -- a patchy environment of conifer trees with open spaces containing tundra-type plants -- would have been a favorite grazing ground of the American mastodon.  There is, however, no evidence of people at Mashantucket at this time