Fig. 11. Map of the old volcanic region near Mount Hitchcock and west of the Notch.
The edge of the eastern mountain mass is located at the French King Bridge and passes half a mile west of Montague. Its location beneath the younger fill is known less perfectly farther south, but it seems to extend through Amherst, certainly west of South Amherst and Granby and probably east of the Notch. At least two mountains rose above the ancient lowland floor; the northern one is a long ridge of schist between Bernardston and Mount Hermon, and the other is Mount Warner. Mount Warner is an island of highland rocks in a sea of red sandstone fill. The Bernardston ridge resembles a peninsula in somewhat analogous sedimentary surroundings. The two eminences reveal the form of the valley floor and the western hills at the dawn of the Triassic period, for they were spared from destruction by burial, until deep erosion exposed them again in Miocene time.
Hot Springs in Central Massachusetts
Hot springs the world over register their presence by leaving deposits of unusual minerals, and they have left this sort of record at Loudville. Here the coarse sandstones of the lowland rest upon gneiss, and at the south end of the Loudville lead vein barium sulphate crystals, called barite, formed in the sand before it was cemented into solid rock. The crystals are the product of highly charged mineral water, rising through the sands from a subjacent fissure. The fissure itself is also filled with barite, and with galena and quartz as well. It is the vein which was worked in the old Loudville lead mine. There are other veins in the western and eastern highlands at Hatfield, at the Northampton reservoir near Whately, and at Leverett. All are in fractures which were still partly open when the valley first took form.
The Marginal Uplands
The rocks which formed the high eastern mountain range of Triassic time and the rocks which made the old western hills and underlay the basin floor comprise essentially a single group characterized by its complexity. At one place the rock resembles sandstone, but the layers stand on end; at another, it looks like shale, but the stone breaks across the color banding instead of parallel to it; and at a third place a fissure seems to have opened and had a crystallizing melt poured into it. These tabular, filled fissures can be found nearly everywhere, coursing in every direction and at all conceivable inclinations to form a network that binds the older rocks into a firmly knit whole. The fillings, or dikes, are like reinforcing rods, holding the rocks together and withstanding the agents of destruction. Thus, the story of the highlands has three distinctive phases,—a relatively young phase when the interlacing reinforcements were poured into fractures; a somewhat more remote stage, when the bedded rocks were crumpled into their inclined positions; and an earlier stage, when the bedded rocks were deposited. The geologic dates of these three events may vary from one locality to another, and they certainly are different in the Eastern Upland as compared with the Western Upland; but the events always occurred in this sequence and constitute the broader aspects of the story at all places.
Fig. 12. Block diagram showing topography during formation of the lead veins.