Dana holds that the throw of the waters against the right bank of a stream (the western if flowing south, or the northern if flowing west), in consequence of the earth's rotation, may have had its effects, and may possibly account for the cases in which the western side is the steep one, notwithstanding a vertical or even a high eastern pitch.

The lime-stone belts of the county are divided by Prof. Dana into: 1st, the Southern section of the county, from New York Island to White Plains ; 2d, The 3Iiddle section, from White Plains to Croton Lake ; and 3d, the Northern section, north of the Croton Lake.

The southern section is composed of three areas or belts which, commencing in New York Island, extend for two or three miles into Westchester County. The tirst of these areas, the Trcmont, extends from Fordham southward to Harlem River, and thence into New York Island. It reaches the Harlem River by two lines -- a western at Mott-Haven and an eastem at the mouth of Morris Hill Brook, west of Brooke Avenue. The second belt of the southern section, that of "the Clove" follows Cromwell's Creek, north of Central (or McComb's Dam) Bridge and the brook emptying into it. The most southern outcroj) occurs about a mile north of the Bridge; it again outcrops near the " Club House." This belt probably continues southward into New York Island. The third area of the southern section is a prominent feature of the north end of New York Island, from which it extends three miles northward into Westchester County along Tippitt's Brook. The Harlem River makes a deep cut through it at Kingsbridge; and where the abutments of High Bridge rest, disaj)- pearing there, outcrops at points in Tipj)itt's Valley as far as nearly three miles from Kingsbridge.