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Published online by Cambridge University Press: 01 May 2009
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.
Page 62 note 1 A slide of this rook in the collection of Dr. Teall was examined, with his kind permission, by Miss Heslop; it is marked “Tachylite, 3½ miles east of Greenhaugh”, and contains well-formed porphyritio augites (with large optie angle) not unlike those of the Cleveland Dyke, but they are pierced by groundmass felspars.
Page 65 note 1 “On the Crookdene and Related Dykes,” by Miss Heslop, M. K., M.Sc, and Dr. Smythe, J. A., Q.J.G.S., 02, 1910.Google Scholar The suggested explanation of the micro-crystalline groups given in this paper has received support from subsequent observations, and especially from the case under discussion. Dr. Teall very kindly lent me some slides of the North of England dykes, and one was found to satisfy almost perfectly the requirements of a semi-vitreous marginal solidification, which had been broken up into more or less angular fragments by a later re-heating. In this case the fragments consisted of devitrified glass, in which were embedded various elementary crystals, while they (the fragments) were embedded in a similar devitrified glass with some quartz.—M. K. H.
