It is in accordance with this that the least degrees of metamorphism are found in the lime-stone and associated schists of the vicinity of Peekskill, in the northwest corner, while along the central and eastern portions of the county, and in the western, also, south of the Croton, the crystallization is commonly very coarse; that the lime-stones have the same kind of associated rocks -- that is, of mica-schists and gneisses -- as the eastern and more metamorphic portions of the region in Connecticut ; that the lime-stones have a like paucity in disseminated minerals and similar occurring species with those of Connecticut ; and that the ordinary normal trend of the rocks -- north 10° east to north 20° east -- is very nearly the average trend of the beds of lime-stone and associated rocks in the Green Mountain system.

Prof. Dana's conclusions are that : " The lime-stone of Westchester County and New York Island and the conformably associated metamorphic rocks are probably of Lower Silurian age."

The soils of the county are made up of the abrasions and disintegration of the gneiss, feldspar and lime-stone rocks, with considerable districts largely composed of sand and more limited areas of clay. As a whole, the soil may be called a light loam. It is generally favorable to the growth of cereals. The valleys have the addition of vegetable matter and are very productive of the rich natural grasses which abound here. The hillsides have suffered I'rom washing by heavy rains, but yield abundant crops to good cultivation. About the hill-tops and along the .summits of the ridges the rocks generally crop out, so that these localities are mostly left to be covered with forest growths, adding greatly to the beauty of the scenery. In many places in the county there are peat swam2>s, where ancient lakes have been tilled with the accumulation of vegetable matter and the growth of sphagnum moss.