The flow of time in the Connecticut valley

by George W. Bain; Howard A. Meyerhoff

b. Volcanoes ejected much ash and many bombs to form the Granby tuff.

Some of these three-toed animals were like the modern lizards and walked on all four feet; but the great majority walked on two feet and, like the kangaroos, used their tails to balance their bodies, and their short fore limbs to support them when they crouched. In any single playa deposit, variations in the sizes and kinds of footprints reveal that many individuals made them; yet strangely, most of the tracks at any one place are headed in a single direction. Apparently the herd instinct must have been strong in these reptiles, as it is in kangaroos or in a flock of turkeys, all following a leader, with only an occasional individual going off to one side or back-tracking in a display of independence. And so the dinosaurs dominated the life in the early Connecticut basin, as it sank and trembled, and as mountains rose to the east; on dry days and days of cloudburst, on hot days and days when frost crystals formed in the mud, they roamed the plain, as the lowland settled nearly two miles and filled to the brim with red sands, muds, and marginal gravels.

Volcanoes

Red is the predominant color in the central inlay of the New England design, but greens and blue-black lines have been worked into the pattern. The dinosaur-ridden basin has a rim south of Middletown in Connecticut, and another north of Holyoke in Massachusetts; it lies just west of the dinosaur-track ledge near Holyoke, and the tracks themselves are only thirty feet above the bottom of the basin. The rim is an odd ensemble—now red and now green; here solid and hard and black, there soft and fragmental and crumbly. The fragments may be angular or round; sandy or glassy; dense and solid, or full of bubble holes like molasses taffy. The whole looks like the spread-out ash dump from a giant power plant. And not only does it resemble an ash heap—it is the ash heap of a volcano; and the hard black layers within it are lava flows interspersed with the heavy falls of ash.

Fig. 8. Map showing agglomerate burying a fault scarp on the power line through the east gap of the Notch.

The ancient ash heap grows thicker east of the Connecticut River, and it is more than 3,000 feet from top to bottom around a series of massive blue-black rock-columns southeast of the Mount Holyoke Hotel. These are the lava-filled necks of craters which became quiescent with the dawn of the dinosaur days. The ash deposit, called the Granby tuff, grows thinner eastward away from the craters and disappears completely northeast of Granby, where a stream deploying from a valley in the eastern mountains washed it away as fast as it fell and left coarse gravel in the form of a huge fan.

The floor on which the ash came to rest was not everywhere the same. Where now it crosses the Northampton-Holyoke highway and the Amherst-South Hadley road it was a lava flow; but north of Granby and at numerous places between the Hockanum and Amherst-South Hadley roads the ash lies on conglomerate. Along the Amherst-Springfield power line, a block of the conglomerate floor was pushed up five hundred feet above the same beds farther west, forming a small block mountain which was entirely buried beneath the ash. Similar block mountains can be observed under the blanket of ash, especially on the south side of the Holyoke Range; and renewed movement subsequently affected many of the blocks north of Granby, where the ash deposit and even some of the sediments laid down in the earlier days of the dinosaurs were fractured and displaced. As a rule, along any one fault, the block on the east was pushed up and moved southward; and the block on the west was pressed down: as a group, the fractures may form the beginning of the great eastern border fault which bounds the basin farther south.

The volcanoes which made the Granby tuff or ash bed erupted intermittently for a long period of time. Usually, the river which emerged from the eastern mountain range brought so much fluvial debris that ash is not in evidence except in the immediate vicinity of the craters located between the Notch and the summit of Mount Holyoke. Even though alluvial sands and gravels supplant the tuff here and there, the river did not succeed in closing or quenching those fiery vents. The rocks now present recount a struggle in which, at times, the river encroached upon the cinder cones; at others, the ashes choked the stream and buried its alluvial wash.