STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

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(Ruedemann, 1947), the best opinion today is that the Norrnanskill is post-Chazy in age, that it probably ranges from the Black River into the Trenton epoch. The Pre-Ordovician Unconformity The Schaghticoke ?-Deepkill ?-Normanskill strata in the Castleton area lie in a few places on Mettawee, in many places on Schodack, in one place on Zion Hill, and in one area on the Nassau formation. "At a point IY4 miles north-northwest of Chamberlin Mills, Mr. Prindle finds Hudson graptolites in black shales within 15 feet of the Olive grit [Bomoseen] of the Lower Cambrian" (Dale, 1899, p. 189). Throughout the slate belt "the Calciferous [Schaghticoke-Deepkill] is not certainly everywhere present and the Ferruginous quartzite [Zion Hill] is intermittent, so that in many places but a few feet intervene between the Hudson graptolites (Normanskill fauna) and the Olenellus fossils. In other words, the Middle Cambrian (Paradoxides fauna) and the Upper Cambrian (Potsdam sandstone) are wanting and the section passes at once from Lower Cambrian to Ordovician, and that not at one exceptional locality or along one line or plane of fracture, but at many exposures along intricate boundaries separating masses of complex folds. Another equally striking fact is that the Lower Cambrian and he Ordovician, wherever their contact is fairly well exposed, occur in apparent conformity ......(p. 291). Erosion of some of the Cambrian before the deposition of the Lower Ordovician strata will explain these facts. There need not have been significant diastrophism before this erosion. No proof exists that Middle and Upper Cambrian beds were not deposited before this erosion; but no rocks of such ages have been discovered in the Taconic sequence, with the exception of limestone boulders in the Metis shale and other formations in Quebec (Rasetti, 1946, p. 703, 1945a, p. 62-63, 1945b). Red and green Normanskill slate ; Normanskill grit, and Berkshire schist "all come together," according to Dale, on Rupert Mountain in Rupert, Vermont. Dale believed this to be additional evidence of an Ordovician age of the Berkshire. If most of the Berkshire schist is of Nassau age, as it is considered here, the finding of Normanskill near Nassau signifies that pre-Ordovician erosion cut down into the Nassau in some places. Judging from Dale's comments, the boundary between the Ordovician rocks and the Nassau formation is easier to map than the boundary between the Cambrian and the Nassau. This must be because 57
the former is an unconformity and the latter is only a gradational sedimentary boundary between the Bomoseen and Mettawee above and the Nassau below. DIKES General A few mafic dikes are the only igneous rocks in this area. The classic papers on the dikes of this region are those of Kemp and Marsters (1889, 1893). A complete account of the dikes of the slate belt of New York and Vermont is found in Dale's report (1899, p. 222-226). Twenty-one dikes lie within the Castleton quadrangle. The dikes are most prominent in the northwestern part of the quadrangle, an area that was examined only in reconnaissance during this investigation. The dikes range from a few inches to 40 feet in width and from about 20 feet to 3.25 miles in length. Most of the intrusives are only a few hundred feet long, but two great dikes 2.75 and 3.25 miles in length are prominent features east and west of Lake Bomoseen. Each dike appears to follow the joint system that is locally best developed in the country rock. The trends of the dikes of the Castleton area have no noticeable system. All dikes have steep dips. Although Dale believed that a genetic relation exists between diagonal joints and dikes, he recorded strikes of the dikes in the slate belt in all directions. Bain (1938, p. 4-5) found a northeast strike predominating in the marble belt. Petrography The dikes of this area are chiefly camptonites, augite camptonites, and diabases. In the slate belt in general Florence Bascom, as quoted by Dale (1899), found 34 augite camptonites (some approaching diabase), 14 camptonites, and 7 analcimites. From the marble belt east of the Taconic Range Bain (1938) listed minette, vogesite, and kersantite as additional types. Most of these dikes are referred to the lamprophyre family. During the present survey 4 small dikes were found, in addition to the 17 previously described. Brief descriptions are as follows: 1. Augite camptonite in a dike 8 inches wide. Traced 30 feet; appears to peter out. Attitude: N 550 E, 800 S. Location: Bottom of northernmost "Westland" marble quarry southwest of West Rutland athletic field. Country rock: Beldens formation. This rock is dark-blue-gray with 1-mm. white dolomite (?) amyg - 58
Page 1 and 2:
STRATIGRAPHY AND STRUCTURE OF THE C
Page 3 and 4:
PAGE Schodack formation ...........
Page 5 and 6: eak thmst. The Taconie sequence is
Page 7 and 8: Much of the Castleton area is occup
Page 9 and 10: Walcott (1888, p. 235) discovered O
Page 11 and 12: VALLEY SEQUENCE TACONIC SEQUENCE 0.
Page 13 and 14: The composite thickness of the Vall
Page 15 and 16: east of Lake Dunmore Foye (1917-191
Page 17 and 18: in the Cheshire (Keith, 1923-24, p.
Page 19 and 20: genera as Olenellus, Nisusia, Kutor
Page 21 and 22: egarded as eastern facies of the Po
Page 23 and 24: of very small and very large dolomi
Page 25 and 26: The "lower 10 to 40 feet of the Col
Page 27 and 28: directly above the Columbian marble
Page 29 and 30: West Rutland are among the most bea
Page 31 and 32: Thickness and age: The Orwell in Ir
Page 33 and 34: Age: Many crinoid columnals and oth
Page 35 and 36: northeast of Chippenhook the Whippl
Page 37 and 38: westward so as to overlie the strat
Page 39 and 40: elow under "Relations and correlati
Page 41 and 42: grains came from veins and some fro
Page 43 and 44: assume at least a ten-fold thickeni
Page 45 and 46: poraneity. Vaughan and Wilson (1934
Page 47 and 48: flattened in the plane of the regio
Page 49 and 50: andesine grains, slate fragments si
Page 51 and 52: teristic rusty appearance of the we
Page 53 and 54: Kaiser (1945, P. 1089) discovered a
Page 55: skill in the Castleton area. Severa
Page 59 and 60: 30 0 C a- S In w 0RWE 7 Rusr THI I0
Page 61 and 62: West Rutland anticline and adjacent
Page 63 and 64: that Keith mapped at the northern e
Page 65 and 66: folds in the Taconic sequence. Had
Page 67 and 68: erosion the Taconic sequence overla
Page 69 and 70: where more competent beds cross the
Page 71 and 72: Silurian time. Under the present hy
Page 73 and 74: dolomites of \ermont from red at th
Page 75 and 76: tion of the Cheshire. Sands from a
Page 77 and 78: much of the New England region. Pie
Page 79 and 80: REFERENCES CITED AGAR, W. M. (1932)
Page 81 and 82: (1941) The Taconic allochihone and
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STRATIGRAPHY AND STRUCTURE CASTLETON AREA VERMONT

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