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 VERMONT 313 of the Laraoille river. In June, 1810, an at- tempt was made to open an outlet from it to Barton river on the north, when all the water of the pond, which was 1^ m. long and J m. wide, tore its way through the quicksand, which was only separated by a thin stratum of clay from the pond, and advanced in a wall from 60 to 70 ft. high and 20 rods wide, car- rying everything before it, reaching Lake Mem- phremagog, 27 m. distant, in about six hours. There are several islands in Lake Champlain and one or two in Lake Memphremagog be- longing to the state ; the largest are North and South Hero and Isle la Motte in Lake Cham- plain, which with the peninsula of Alburg constitute Grand Isle co. The only consid- erable harbor is that of Burlington, on Lake Champlain. The geological formations of Ver- mont consist chiefly of the lower groups of the geological column comprised in the azoic and Silurian divisions. The Devonian forma- tion is represented by a band of limestone about a mile wide and 20 or 30 m. long on the E. side of the Green mountains. The drift formation overspreads the whole state, and al- luvial deposits of limited extent are met with along the banks of the rivers. The lower for- mations are all of uncertain age, owing to the metamorphic character of the rocks, their doubtful stratigraphical relations, and their dearth of fossils. Their determination has been an interesting subject of investigation. The Green mountain range is composed chiefly of gneiss, which may be the oldest rock in Ver- mont, or may prove to be of Silurian or Devo- nian age, or both in a metamorphic condition. Should this prove to be anticlinal, the group will then pass on each side under rocks of later age; but if its structure is synclinal, it then overlies the rocks on either side ; so far it has been found impracticable to determine this question. Along the "W. base of the Green mountains extends a great belt of quartz rock, which in the opinion of the surveyors rests upon the gneiss, and which has been sup- posed to be the equivalent of the Potsdam sandstone, though now regarded by the Ver- mont surveyors as of the age of the Medina sandstone of the Clinton group of New York. Apparently overlying this is a great bed of crystalline limestone 2,000 ft. thick called the Eolian limestone, from Mt. Eolus in the S. W. part of the state. This has been generally re- ferred to the lower Silurian group, but its true position in the geological series is very doubtful. The rock constitutes the principal portion of several ranges of mountains in the S. part of the state. Along Lake Champlain the rocks are lower Silurian and primordial, slates found in the town of Georgia being re- ferred to the latter system on the evidence of trilobites discovered in them. The Laurentian group is represented in a small exposure near Whitehall at the S. extremity of Lake Cham- plain. Various mineral productions of value are found in connection with the ancient for- mations of this state. The talcose slates and quartz rocks, as throughout the whole range of the Appalachian chain, present numerous deposits of hematite iron ore. The same for- mation has also furnished productive mines of manganese at Chittenden ; and at Plymouth and several other places it has produced gold. Lead ores, more or less argentiferous, have been found at several localities along this range, but have not proved profitable. At Vershire and Corinth, Orange co., is a large vein of pyritous copper ore. In the serpentine rocks about Troy, in the extreme north, chromic iron has been met with in considerable quan- tity. Excellent clay for white stone ware has been worked for the pottery at Bennington, and beds of soapstone are found in many towns along the central N. and S. line of the state. Vermont is rich in marble and slate. Marble was first quarried at Rutland in 1844, and the quarries there now supply about half of the production of Vermont. The marbles obtained are the white statuary and the variegated, mot- tled, and blue. The proportion of white is larger than in any other part of the state ; it is not inferior to the best Italian. The Suther- land Falls and East Dorset quarries produce marble resembling the veined Italian. The Swanton and Isle la Motte marble when pol- ished is jet black. The Lake Champlain quar- ries produce marble resembling brocatella. Wi- nooski yields fine Siena and other grades of pale red and white. There are valuable slate quarries in Rutland, "Washington, and Wind- ham counties. The first quarry was opened at Fairhaven, Rutland co., in 1845. For many years the production was inconsiderable ; but this industry has now become important in consequence of the increased demand for roof- ing slates, floors, tiles, &c. In 1875 the produc- tion was valued at $370,000, being chiefly from the Fairhaven quarries. The state abounds in beautiful waterfalls and other natural curiosi- ties. The most remarkable, besides Bellows falls in the Connecticut, adjoining a village of the same name in the town of Rocking- ham, but belonging to New Hampshire, are the " Great falls " on the Lamoille in Milton ; the McConnel's falls, and the natural bridge a little below them, in Johnson; the "Great falls " on the Clyde in Charleston, where there is a descent of 100 ft. in 40 rods ; the numer- ous falls on the Winooski, with its natural bridge and caverns in Duxbury ; the magnifi- cent fall of 70 ft. in the Missisquoi at Troy, and the gentler one at Ilighgate ; the falls in the Passumpsic at Lyndon; the falls in the Black river at Springfield; and the caves at Dorset and Plymouth. The climate of Ver- mont is severe, and the winters are cold ; but there are not many sudden changes, and the state is remarkably healthful. Observations at Lunenburg (lat. 44 28', Ion. 71 41', elevation 1,210 ft.) show the following average means for 25 years: January, 16-54; February, 17'38 ; March, 26; April, 37-86 ; May, 52-18; June,