Page:The Journal of geology (IA journalofgeology21894univers).pdf/431

briefly mentioned. Along the south slope of a hill just south of Mechanicsville, a section is exposed showing fine-grained biotite gneiss at the base, passing imperceptibly into a sugared quartzite above. This in turn is overlain by coarse saccharoidal limestone; and a muscovitic, garnetiferous schist overlies this, capping the summit of the hill. These rocks strike in general east and west and dip northerly. A section on the southwest slope of Ludlow Mountain, two miles southeast of here, exhibits at least two beds of coarse limestone grading into tremolite and green hornblende, interstratified with layers of schist. These rocks strike west of north and dip easterly. On the southwest slope of Saltash Mountain a bed of tremolitic limestone interstratified in biotitic gneiss trends northwest. At Northam village, a similar coarse limestone occurs associated with a vitreous quartzite, a laminated eruptive rock and a rusty muscovitic schist. All through the core there are patches of these coarse limestones in a great variety of association, such as with coarse augen-gneisses (a common occurrence), quartzites, schists, and other rocks. Fine-grained, blue marbles are present in two or three localities. In all cases the limestones are in irregular lenses, and are extremely local; their occurrence with coarse gneiss affords no evidence of structure; these scattered, irregular outcroppings and differences of association make them impossible of correlation. There may be two horizons of limestone in the core or there may be a dozen. The same is true of the quartzites and other sedimentary rocks. Limestone belts are, however, frequently identified by their metamorphosed equivalent, tremolite, or in rare instances, serpentine replaces the limestone. The Mount Holly series has scattered all through it these undoubted areas of sedimentary rocks recognizable where from manifold causes they have escaped destruction or metamorphism, and their clastic characters have not been obliterated. They probably represent remnants of a once great sedimentary series older than the Mendon series.

The rocks associated with the evident clastics present a great variety of texture and mineral composition. Thin sections show, however, that the differences are mainly due to variations