III.—The Tachylite of the Cleveland Dyke

Abstract

The Cleveland Dyke is well exposed low down on the left bank of the River Tees, near the junction of this river and the Lune, being washed at flood-times by the water. It trends in a direction north of west, and can be traced for a distance of several hundred yards: its thickness is difficult to estimate as the north edge is covered by drift. The tachylite variety of the rock is only exposed for a few yards, and has only been found at this point—about 100 yards west of the junction of the Lune and Tees. The dyke here appears to occur in sheets very like successive lava-flows, and during cooling a columnar structure has been developed and the bases of the columns, mostly hexagons, face the river.