312 STRATIGRAPHICAL GEOLOGY. 



Viewed in a general way, the slates appear as a single basin, with a 

 normal synclinal dip evident at the south end. Older rocks have pro- 

 truded themselves into the midst of the slates, having been pushed up 

 from below through lateral pressure, thus punching holes, as it were, 

 through the more yielding material. As a whole, the dips along the 

 borders have not been affected, though there are many local exceptions. 

 Often, where limited patches of the slate remain, their dips conform to 

 the synclinal disposition. If the underlying rocks have been thrust 

 through the slates near the eastern border, the remnants preserve their 

 proper north-westerly dip ; or, if the disturbance has been upon the west- 

 ern side, we discover the normal south-westerly dip remaining. At the 

 south end of the formation in Bath, the pressure has been so great that 

 the strata stand nearly upon their edges. The general attitude is anti- 

 clinal, dipping 80° south-easterly by S. M. Lang's near the eastern border, 

 and north-westerly near the junction with the western schists near B. C. 

 Child's. Yet the underlying schists conform to the proper basin struc- 

 ture, dipping north-westerly at the town-house, and south-easterly at W. 

 Lang's, west of B. C. Child's. . The altitudes of the lower and upper 

 series are portrayed upon Fig. 29, Plate XIII. 



The lithological aspect of the slate is uniform all over the basin. 

 Analyses by Prof. Seely indicate a close similarity between these slates 

 and the argillitic mica schists of the Lyman group in their ultimate 

 constituents, so I have suggested the derivation of the former from the 

 degradation of the latter. The slate at the Dodge mine gave, — silica, 

 72.98; peroxide of iron, 6.35; alumina, 5.99; magnesia, 0.36; potash, 

 5.61; soda, 9.92=101.21. Veins of auriferous quartz and an occasional 

 thin bed of quartz conglomerate are the chief foreign rocks present. It 

 is likely that careful analyses of the slates from different parts of the 

 basin would show a considerable variation in composition, especially in 

 the amount of silica. The constancy of mineral composition may be a 

 useful guide to us in distinguishing between the Cambrian and Helder- 

 berg slates, where they come into close contact with each other. 



Excursions along the eastern border of the slate in Bath show a uniform north-west- 

 erly dip between the Lyman line and the nearest road crossing it to Bath village. At 

 the tunnel, or ancient mining excavation for coal opposite the south end of the aurifer- 

 ous conglomerate, the dip is 30° N. 42° W., the rock being black and carbonaceous. 



