Only once did the volcanoes dominate the situation in the valley, and that was very early in their history. A group of vents, localized along a southward trending zone about a mile west of the Notch, and another group along the present course of the Connecticut River from Turners Falls to Sunderland poured out billions of cubic feet of black basaltic lava into the center of the lowland. Eruptions followed in such rapid succession that the rivers never scoured the surface of the earlier flows. Lava piled up 400 feet thick in the center of the basin east of the Mount Tom Range; it moved eastward in a flow which thinned against the fans of rivers issuing from the eastern mountain, and it ended in a formidable wall of scoria confronting the mountain streams. Lava buried the northern basin from Sunderland to Turners Falls and beyond, while the southern basin filled from Northampton to New Haven. But lava dominance was short-lived, and even before its bubbly surface reddened to the weather, streams had covered it with gravel. The lava flows are the most resistant materials used in the lowland design. They form the ridge east of Greenfield in the northern basin. The Holyoke and Mount Tom Ranges are remnants of these flows, tilted at moderate but varying angles by the recurrent movements which enlivened the epoch of dinosaurs and volcanoes. [Illustration: Fig. 9. _Block diagram showing the main features of central Massachusetts during volcanic stage._] [Illustration: Fig. 10. _Block diagram showing the Triassic basins of central Massachusetts._] The most spectacular episode of lava extrusion was localized in a small volcanic center situated about one mile west of the Notch in the Holyoke Range. All flows in the range moved away from this center, and before the great outpouring took place, minor explosive outbursts had built cones of ash with bases up to a mile in diameter. Small lava tongues are interspersed with the ash beds, and mixtures of sand and lava tell of breaks through the 1,500 feet of sandy fill which was rapidly accumulating in the basin. Throughout this early period of volcanic activity the streams brought out so much wash from the eastern mountains that they soon dominated the scene in Massachusetts, and in Connecticut volcanoes gained ascendancy for one brief moment of geologic time, when an early flow covered much of the valley from Hartford south. _The Original Valley_