Bernard a. Drew: Hoosac Tunnel offered quite the core sample
GREAT BARRINGTON >> Geologists trying to figure out our underlying rocks, more than a century and a half ago, worked with what they could see. James Dwight Dana (1813-1895) of Yale, for example, gleaned considerable information about gneiss, schist and quartzite strata in Great Barrington in 1877 thanks to what he found in a quarry. Monument Mountain in Great Barrington, an inverted tectonic burp, shows itself off well and T. Nelson Dale (1845-1937) of Williams College wrote an informed paper about it in 1895.
Harvard University minerologist John Eliot Wolff (1857-1940) took advantage of construction of the Hoosac Tunnel between Florida and North Adams to look for clues to the structure of Hoosac Mountain.
Born in Montreal, Wolff graduated from Harvard in 1879 and earned his Ph.D there a decade later. He taught at the institution starting in 1923, taking time off to work for the U.S. Geological Survey and to lead the Mineralogical Society of America. He was curator of the Museum of Natural History. He also taught petrography, the microscopic examination and classification of rocks.
Wolff came to North Berkshire in 1895. As The Transcript reported Oct. 12: "A party of geological students from Harvard university came to North Adams yesterday with Prof. J.E. Wolff of the United States geological survey to study the geology of Hoosac mountain, and especially the interesting structures shown by the accumulation of rock which was drawn from the central shaft of the Hoosac tunnel."
The tailings from that vertical bore constituted an enormous core sample.
Continued the newspaper: "There were fourteen in the party, some of whom arrived on the 1.29 p.m. train and the others on the 8 o'clock evening train. One of those who came in the afternoon took quite a tramp before night, going some distance up the mountain to the northwest of the town and then crossing the valley, and going up to the 'Bellows Pipe.'"
This scholar was obviously looking to brownie-up to his teacher.
"The party stopped at the Mansion house," — the four-story Mansion House was on State Street near the union depot — "and this morning they left on the 9.15 car for Adams, intending to walk over Hoosac mountain."
The 4.75-mile Hoosac Tunnel, 24 years in construction, bore through Hoosac Mountain, which "has two crests or summits with a valley between them," Scribner's magazine said in December 1870. "The Hoosac river washes the western base and the Deerfield River the eastern; and it is a curious fact that these rivers are at precisely the same height above tide-water, making it necessary to enter the mountain on each side at exactly the same elevation. Most of the tunnels heretofore built are upon an ascending grade; and it is necessary that there should be some descent in order that the water, which is usually met with in large quantities, may be carried off. In this case the only method of securing proper drainage was to have a summit at the centre, from which the grade should descend to either portal. Accordingly the grade rises about twenty feet in a mile toward the summit level in the heart of the mountain. But this manner of constructing the tunnel" — laborers simultaneously worked from each end to the center, and from the center toward each end — increased the difficulties of ventilation...."
Thus the central shaft, after the tunnel was completed, served as a giant vent.
Wolff reported in Geology of the Green Mountains in Massachusetts, "The rocks of this region are thoroughly crystalline, but little trace remaining in general of their original elements, whether of detrital or eruptive origin, but the bedding corresponding to the original planes of deposit is well marked, and, under the proper conditions, we can therefore determine the order of succession."
He said, "The basement rock is a coarse granitoid gneiss, forms the core of Hoosac mountain proper, occupying the surface of the mountain for several miles, then disappearing below the overlying rock, but cut in Hoosac tunnel for nearly 5,000 feet; hence this rock figures prominently in the dumps of the tunnel shafts." Above this there was considerable Stamford granite, also colorless feldspar, black mica and quartz, the latter "characteristically blue, but when crushed by pressure in the rock is often white or sugary in appearance."
The geologist said information is inconclusive, but the mountain may have been "an eruptive granite modified by metamorphism. On the other hand, its field relations show its close association with and frequent transition into coarse gneisses which seems to form part of a detrital series."
I don't know enough about rocks to interpret what he's saying.
"The rocks thrown out from the 'well' shaft, a few hundred feet west of the west shaft of the tunnel," Wolff said, "are typically of this [gneiss] variety. In the hand specimen the rock is a fine grained, evenly banded gray gneiss; the minerals are arranged in layers and the rock is filled with little squarish feldspars."
He also noted Hoosac schists and Rowe schists, Vermont white gneiss quartzite conglomerate, Stockbridge limestone and Hoosac gneisses
Wolff had found a rock-lover's heaven.
Jack Trowill of Berkshire Scenic Railway tipped me off to a fascinating video of the interior of the tunnel. It was made Oct. 25 and on Youtube and is called "Hoosac Tunnel Ride Through — W to E — Infrared Footage - Best known Hoosac Footage!!!"