Mineral Industries and Geology of Certain Areas - Vermont Agency ...

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I 74 REPORT OF THE VERMONT STATE GEOLOGIST. deposit of ore incl:easing in dimensions as you go below the surface. However, the opposite is possible, for the surface content is very small. GEOLOGY. MU ! ONO -- 1T . w -. The architecture of the heterogeneous terranes of Orange county. Vt.. is somewhat obscure. The original horizontal series of sands, gravels, clays, and mans have their modern representatives in tilted and crumpled schists, argillites, limestone and crystalline marbles. These rocks have been compressed into great folds with a huge anticlinal along the center of the crystalline marble, with minor anticlinals and svnclinals tlPOfl either side. As a direct result of this compression, linked with the injection of igneous material, many new minerals have been developed and the countenance of the original deposits disguised. Planes of cleavage were induced at varying angles with the lines of original bedding and the Lower Silurian rocks superimposed unconformablv upon Huronian terranes. - ..4 A. Jill IIURONIAX. The outer flanks upon the east and the west are Huronian. No attempt is made in the protracted sections to plot the western member save as it comes in contact with the Montpelier slate. The eastern member is plotted only to the Connecticut River. The former is largely hyciromica and chlonitic schist with beds of serpentine and soapstone as alteration products. These rocks are often studded with crystals of magnetic iron. The latter is of the same general nature and often highly garnetiferous. On the west side is found a light gray, fine graineci economic granite in Braintree. The largest deposit is on Nevin's Hill. In fact the hill is all granite. Similar deposits are found in Moretown and Northflcicl. The eastern member carries two large bunches of metamorphic fluorite—the larger in Hartford, and crops out in abundance on the left of the road from Christian Street to Hartford I,.. • , • _______ _________ r:J • y.
76 REPORT OF THE VERMONT STATE GEOLOGIST. 4 REPORT OF THE VERMONT STATE GEOLOGIST. 77 village. The smaller is in Newbury to the east of Hall's Pond. and found in Washington, 25 miles distant, a dike one foot wide, Each contains large crystals of feldspar. with the same cardinal direction, the same concretionary de- Two bunches of protogene gneiss grace this member.* The composition, lithological similarity, and microscopical characsmaller is in Newbury on the Ox Bow, the larger in Bradford. teristics. Presumably it is the reappearance of the same dike. b and Fairlee. It is the material of Bradford and Fairlee cliffs. The best exposure is just hack of the hotel at Fairlee. The B. cliff rises by almost perpendicular ascent for about 200 feet; SLATE. while at its base is a large talus of broken fragments of gneiss. The material is unlike the pi -otogene gneiss of Hanover and The second pair of parallel terranes, lying within the old Lebanon, N. H. The mica is xnore abundant and the paral- Huronian deposits, have long been called Cambrian. They lelisni greater at Fairlee and Bradford. At Hanover the mica are narrow bands of soft, black, fissile, arenaceous slate resting is chlorite and the gneiss is brittle. It is not impossible that at unconformably upon the Huronian schists. The western band Fairlee we have the relics of an extinct volcano. A narrow belt begins near Lake Memphremagog and suddenly terminates of hydromica schist lies between the cliff and Lake orev. near Barnard Village. In Braintree, Brookfield, Williamstown The lake is entirely in slate and the crests of the adjacent hills and Berlin it is interstratified with the Washington limestone, are Bradford schist. and is referable to the same age, viz: Lower Trenton. Its Near the Connecticut River the Huronian schists are nearly highest development is in Montpelier and Northfield, where it vertical and ofttimes much crumpled. In Newbury there are has been extensively quarried as a fine roofing slate. Although at least three synclinal troughs and two anticlinal axes. the Montpelier quarries have been abandoned, those at North- Thetford there is one of each. In Fairlee the dips are all field are successfully operated by the Dole-Brill Slate Company, between 85 ° and 900 slightly to the east. which produces a fine grained, excellent, permanent block slate. In the summer of '96 there was reported to me from Newbury Few, if any, quarries in the State have less waste. an Indian burying ground, situated about two miles north of The general strike of this member is north 10° east. In Newbury Village, in a cut on the Passumpsic Railroad. Braintree and Randolph, north and south. In Bethel, north and visit to the locality proved this Indian cemetery to be an inter- south and north 100 west. In Barnard it becomes a narrow esting dike of diabase about i8 inches wide and exposed to a. line with strike north and south. height of Jo to 12 feet above the track. The peculiar interest One-half mile east of the city of Montpelier are the slate . attached lies not in lithological characteristics, for herein it is quarries of James T. Sabin. They have been worked to a depth not unlike many trap rocks, but in its striking surface decadence of ioo feet. along multitudinous planes of fracture. The resultant presents In November, 1896, I visited the slate quarries of Northfield the appearance of a stone wall set on end. The decomposing in company with Dr. C. H. Hitchcock and F. F. Austin, to disboulders lose their concentric shells, reveal the structure of a cover, if possible, illustrations of planes of original bedding in contradistinction to the superinduced planes of cleavage. The concretion, and ultimately remain as granules of coarse sand. The dike runs east and west. I tried to trace it over the hills highly satisfactory results were subsequently published by Dr. Hitchcock in a Bulletin of the Geological Society, Vol. VIII, "These areas do not show well on the map. The word Gneiss printed on the . - id 289-390, in which he describes kindred phenomena in the margin indicates the localities.
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