Preliminary Report on the Geology of Franklin County.

G. H. PERKINS.

Franklin County occupies the northwestern corner of the state. Consequently its northern border is also the Canadian border and its western border is part of the shore of Lake Champlain. As the Green Mountain range extends through the eastern portion, the surface there is often very rugged and the rocks are largely metamorphic or crystalline.

Thus far the work the Survey has been able to carry forward has been confined to the western border among the stratified rocks. While the geologist has visited numerous localities in this part of the county, mostly in company with Mr. G. E. Edson of St. Albans, who has for some years made a careful study of the strata in and about that place, most of the field work has been done by Mr. Edson. In the Report of 1904-6 a chapter by him on the geology of St. Albans was published with a small map. As will be seen on following pages, Mr. Edson has continued his explorations into Swanton and during the past two years has gone over its area and located the different terranes. Both Mr. Edson and myself have also done some work in Georgia, the town immediately south of St. Albans, and in Swanton, and Highgate on the north.

It is unnecessary to inform geologists that the rocks of much of the western part of Franklin County have long been under consideration, especially in the discussion of the Taconic question. Aside from this at one time much mooted subject, some of the beds of Swanton and Georgia, and their fossils, have been of great geological interest. For the most part fossils of any sort are not abundant in the rocks of the region, but there are some layers, or small areas, in which the fossils are numerous and well preserved. The beds are in many places much more fossiliferous than appears to a hasty investigator. For there are layers in which few or no traces of fossils

can be found unless weathered portions can be obtained, and then it is found that the seemingly barren rock is full of fossils which have so exactly the characters of the rock mass that they are wholly invisible unless oxidation has changed the color and condition of both rock and fossil. The rocks of the county occur in great variety, there being sandstones, shales, limestones and conglomerate of different sorts in the western portion, and schists, slates, granites, serpentine, etc., in the eastern part.

It is not to be expected that geological terranes confine themselves within political boundaries, and the fact that the boundary between Canada and the United States crosses the formations which extend from Vermont northward into Canada makes the work of the Canadian geologists in this region doubly interesting.

While some of the views expressed forty years ago would not be put forward today, many of the conclusions expressed in the Geology of Canada, 1863, pp. 272–275 and 854-859, are as important as when first published. I shall, therefore, give the following quotation from Sir W. Logan's account of the geology of the region :

"It has been stated in a previous chapter that what has been called the Deschambault anticlinal, brings to the surface, between St. Dominique and Farnham, strata of the Trenton, the Birdseye and Black River, and the Chazy formations; the exposure being almost wholly confined to a comparatively narrow strip on the east side of the anticlinal axis. The distance between the two extreme exposures is about twenty-five miles and the bearing of the axis, in this distance, is about S. 15° W. If continued in the same direction for eighteen miles farther, it would reach Mississquoi Bay on Lake Champlain and run under the waters of this bay about three-quarters of a mile west of Phillipsburg. From this a gentle turn a little more southward would carry it in four miles farther, to the shore of the same bay, near the Franklin House at Highgate Springs, Vermont. At this spot, strata similar to those of St. Dominique are brought to the surface by an anticlinal, which may not improbably be a continuation of that of St. Dominique and Farnham.

"As already mentioned. the band of Trenton limestone running between these two places is only about a mile from an exposure of the Sillery division of the Quebec group, on the Barbue. The exposures of the Trenton band in this part reach farther south than those of the Chazy, and, approaching Farnham, their breadth gradually diminishes, until they terminate in a point not far from the Yam

aska River.

This arrangement would indicate a gentle slope on the crown of the anticlinal. This would probably bring in higher strata farther south, from beneath which the Trenton limestone would rise again in Mississquoi Bay, to join the exposures near Highgate Springs.

"The natural inference, unless fossils were found to contradict it, would be that on the axis of the anticline, between Farnham and Highgate Springs, we should find the Utica and Hudson River formations.

"The lowest rock brought to the surface on the anticlinal at Highgate Springs, is a dove-gray limestone, similar to that at St. Dominique. It occurs on what is considered the axis of the anticlinal, near a wharf and an old lime kiln, on the shore of the bay, less than half a mile northward from the Franklin House. It is associated with bands of brownish gray, buff-weathering dolomite, from one to three feet thick, and is flanked on both sides by greenish-gray, calcareous, fine grained sandstones. Those on the west side of the axis have a thickness of probably between fifty and a hundred feet, becoming at the top interstratified with greenish shale. No fossils have been found in the dove-gray limestone, but in the upper part of the sandstone there occur one or two undetermined species of trilobites, probably of the genus Asaphus. These sandstones are followed. on each side by blackish, thin-bedded, shaly, nodular limestones, partially magnesian. They are fossiliferous, but the species do not appear to be numerous. Among the fossils met with on the east side

are Ptilodyctia fenestrata, Orthis platys and Ampyx halli, all Chazy species. The thickness of these shaly beds is not certain,

but they probably exceed sixty feet.

"The shaly, nodular beds are followed on each side by about thirty feet of black, massive limestone. Southward from the limekiln these bands, which are about 300 paces apart, run parallel with one another for some distance inland, and then gradually curve around so near one another as to make it probable that they may join, not far beyond the spot where they have become concealed. Both bands hold masses of black chert; that on the west contains Orthoceras recticameratum, O. anellum and O. allumetense, while that on the east has Columnaria alveolata, Stromatopora rugosa, Petraia profunda, Helicotoma planulata, Murchisonia perangulata, and Orthoceras bigsbyi, leaving little doubt that these beds represent the Birdseye and Black River formations. These black calcareous