Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/46

30 in different parts of its course; indeed it cuts across these strata in some places, and alters its relative vertical position to the extent of 1000 feet. There appears, however, to have been more than one eruption, though probably succeeding each other at no great intervals of time: Stanhope, Kirkwhelpington, Ratcheugh, and other places give evidences of this. At Ratcheugh there may have been three eruptions, but two pseudo-strata are distinctly seen there; one of them is wedge-shaped, and, in the course of 500 yards, dwindles down from 90 feet to 30 inches in thickness, while the second mass overlaps the other and is separated from it by 22 feet of intervening limestone and shale. In a pit-sinking at Long Dike, in search of the Shilbottle coal, two layers of basalt were passed through; one, 15 feet thick, is between metamorphosed arenaceous beds; and the other, 63 feet lower down, and 2½ feet thick, penetrates, metamorphoses, and partly replaces a seam of coal.

2. Another mass of trap rock, a greenstone or diorite of considerable thickness, caps the Carter Fell at the height of 1600 feet above the sea level overlying Mountain Limestone strata, which rest on the upturned edges of Cambro-Silurian rocks.

Besides the great lateral dike or dikes, a considerable number of basaltic dikes cut through the Carboniferous strata nearly perpendicularly, most of them having a direction from eastward to westward. The character of the rock of nearly all of them is similar to that of the Whin Sill, but generally finer in the grain, and with the structure more altered by contact with stratified rocks; for at such points there is a mutual transference of character, the basalt itself imbibing, as it were, a portion of the mineral ingredients of the adjoining stratified rock. Of the following basaltic dikes we have some definite information. Our list begins with the most northern.

The Cornhill Dike is seen in a cliff on the south bank of the Tweed, half a mile below Coldstream Bridge, cutting perpendicularly through the Tuedian beds with a direction of north 82°