Fig. 7. Map of Mount Toby showing gorges filled with conglomerate.
Near the northern terminus of the Triassic basin the eastern boundary was not subject to intermittent and violent movements during the later stages of sedimentation, as it was in the south. Instead, the youngest part of the red-rock inlay consists, in some places, of unfractured boulder beds which were washed far out towards the center of the lowland; elsewhere, landslides brought masses of rock debris upon soft red and gray shales, which may have accumulated in shallow lakes; in still other localities, long stringers of red sediment reach far back into the eastern highlands. Many boulders in the conglomerate at the south end of Mount Toby are eight feet in diameter, and torrential mountain streams brought them to their resting place. A few are scratched and grooved, much like the boulders in the till left by the ice sheet; perhaps they signify the presence of snow fields and glaciers in the mountain range, but the scratches may have been acquired by avalanching. The landslide masses buried in the shales at the Sunderland caves show that the mountain front was steep, and the ancient talus or slide rock near the Central Vermont Railroad south of Roaring Brook shows plainly that the mountain front was a precipitous cliff of granite. The stringers of conglomerate extending eastward into the granite upland south of Montague, north of Leverett station, at Amherst, and again near Granby, are alluvial fill in ancient mountain gorges.
This old mountain mass stood out as a long, straight range extending from a point east of New Haven northward into New Hampshire. It was of moderate height in Connecticut, but it became higher and more rugged to the north; glaciers may have nestled around its crest east of Deerfield, and its front was an impressive slope of slide rock. Granite gorges with tapering gravel plains, dry one day and raging torrents the next, fingered eastward into the mountain block. At that time the Connecticut Valley was much like the land east of the Sierra Nevada in California, where greater contrasts in heights and depths are to be found than in any other part of the United States.
A Dinosaur Diary
Like the valley east of the Sierras, the depression in central Massachusetts contained playa lakes and intermittent streams. Sand brought by the mountain torrents clogged the channels and spread into broad alluvial plains, while silt accumulated in muddy lake basins. Black sandy shales now mark the sites of the lake beds, and their black color comes from the coaly remnants of Triassic plants. Some swampy lake margins supported peat bogs, which have been preserved in coal seams two to three inches thick between Granby and South Hadley. Many of the lakes lasted long enough to become stocked with half a dozen species of fish. But the fish led a precarious existence, and their skeletons were buried in great numbers in the upper lacustrine layers when the lakes dried up, and dust and sand drifted over the parched basins at Durham, Connecticut, and at Sunderland, Massachusetts. The remains were interred even more effectively when cloudbursts in the hills brought thick layers of gravel out over the ancient lake beds.
Most of the lakes and ponds were ephemeral, but the fact that their presence was more than a mirage in a Triassic desert is clear from the ripple-marks retained on their sun-hardened surfaces, and from the impressions of objects which touched them while they were still soft. Stray series of parallel furrows record the passing of drifting shrubs, and the abrupt disappearance of rain-drop imprints at a well defined line in the hardened mud marks the exact position of the water level in a few of these Triassic water bodies. Footprints register the activities carried on by a bizarre animal population. Beside the road to the French King Bridge and in the river bed at Turners Falls the ripple-marked surfaces contain the impressions of many feet, and the dinosaur tracks at “the Riffles” beside the Northampton-Holyoke highway are known throughout the country. In Connecticut, Middletown and Durham are famed for their tracks, and the impressions left in the playa beds by muddy feet are so widely distributed throughout the lowland that it must have taken a lot of walking by many generations of dinosaurs to leave such an ample record.
Pl. 4. Rocks of the Triassic basin and their record.
a. A dinosaur walked from the raindrop marked surface at the right to a shallow pond at the left.