Page:The Journal of geology (IA journalofgeology11893univers).pdf/381

Egremont Limestone, and at the south end a reversed fault with the same rock over Cambrian Gneiss. It follows that the throw varies most widely. At some fulcrum point, which must be near the Maltby Quarry, this is practically nil. To the north of that point, the western limb has been downthrown an amount which steadily increases in going north, till in the vicinity of Sheffield it can hardly be much less than a thousand feet. To the southward of the Maltby Quarry, the western limb has been upthrown and the amount of this upthrow at the Cobble must be several hundred feet.

The occurrence of two very thin quartzite lenses, which follow a line parallel with the fault line along "Silver Street" in Sheffield (Cf. Plate V.), is reason to believe that two secondary faults there run parallel to the main fault.

Additional evidence of the main overthrust is the occurrence of numerous very large boulder-like masses of the tremolitic quartzitic dolomite, resting on the Riga Schist to the east of the road on the northeast flank of Miles Hill. It might be argued that they are of glacial origin, since the direction of glacial movement in this section is favorable, but they could only have come from a point just across the river, and such masses are not distributed over the area to the southwest. Such masses are, however, found in abundance along the eastern side of the overthrust for almost its entire length, and it therefore seems most probable that they are fracture blocks produced in the faulting, which have rounded through weathering, and as degradation has gone on, have settled down upon lower beds of the mother rock, and to some extent also upon the Riga Schist west of the river.

This reversed fault presents some analogies with the overthrust faults of the southern Appalachians described by Hayes,^[1] and those in New York described by Darton^[2], but the fault plane