97

stances ; the beds found on the heights arewanting in the bottom of the valley ; thosewhich lie beneath these beds in geological

o C*

order, are not wanting. Sometimes thelower half of a bed is found in the bottomof a valley, the upper half only on its side;followed to the head of a comb, the oppo-site strata approach, unite. This corre-spondence cannot escape the most carelessobserver in those vallies, the walls of whichare precipitous, and at no great distancefrom each other. It often exists, however,though not so strikingly displayed, inwider vallies, where the opposite banks areseparated by large rivers and arms of thesea.

On the opposite sides of the Thames , thegravel and sands of Blackheath correspondwith those of Epping; and the clays ofHampstead, Highgatc, and Harrow, withthoseof Richmond , Wimbledon , and Syden-ham. In Derbyshire, and Yorkshire , we findnumerous insulated summits of millstonegrit, incumbent on a plain, consisting ofmountain limestone. The chalk which pre-vails on both sides the English channel,

H