The rock of which these chains is composed is a dark grey, fine-grained, crystalline, transition limestone, disposed in ho- rizontal strata, which not unfrequently exhibit a very gentldip to the east.

It rests upon a vast mass of talc slate, which dips at an angle of 90° to the east, and forms the outermost member in connection with the higher central range : and farther from this principal chain, it alternates with beds of siliceous and clay slates.

It often contains veins of quartz, but I have never yet found in it any trace either of metals or of organic remains.

These limestone hills form smooth, rounded ranges, which, however, have often a wild and pic- turesque character, from the extraordinary disruption of their masses, and the projection of their bare and steep walls of rock.

They are also clothed with a peculiar vegetation ; and among the isolated outliers of this same formation, are nu- merous lakes.