528 Geological Fotes. By G. A. Lebour, M.A., F.G.S. 



nician that of the Mountain Limestone of Derbyshire. But 

 whereas the Yoredale Eocks proper, and the Mountain Limestone 

 are very different from each other, and can be separated with the 

 greatest ease in their typical districts, the Upper and Lower 

 Bernician are almost identical in lithological characters, a good 

 line of separation between them has yet to be found, their fossils 

 are to a very large extent identical, and their use as stratigraphi- 

 cal terms is one of convenience mainly. So perfect is the faunal 

 identicy of the Bernician Beds, from top to bottom — throughout 

 those ten thousand feet of rock, which Mr W. Topley, F.Q-.S., 

 was the first to announce as being the thickness which this form- 

 ation attains in Northumberland — (6) that Professor De Koninck, 

 the greatest living authority on Carboniferous marine Palaeontol- 

 ogy, correlates the entire series (on the strength of the fossils 

 only), with the Vise Limestone, viz : — the uppermost of the Moun- 

 tain Limestone divisions in Belgium. 



About Elsdon then, we have sandstones and grits forming crags 

 and bold escarpments, shales worn into more retiring features, 

 and limestones tolerably numerous and hard enough, but too 

 insignificant in thickness to show very prominently in the land- 

 scape. To these limestones are due the sinter deposits which 

 have been already mentioned, and to them also are due the swal- 

 low-holes, which are so characteristic of these moors. About 

 Ottercaps and near the Black Stitchel — a hill up the Elsdon Burn 

 — the number of these broad, deep, funnel-shaped grassy hollows 

 following at short intervals the upper line of the outcrops of 

 the various beds of limestone, is simply amazing. Some of them 

 (at the Black Stitchel, for instance), follow the line of subterra- 

 nean streams, emulating in a small way the great river caverns 

 of America, and accumulating a small-pebbled blackish limestone 

 gravel of their own — underground alluvium, in fact, which eludes 

 the mapping powers of the Geological Surveyor. 



The limestones are of the ordinary Bernician character, full of 

 fossils — Productus of many species with Pr. giganteus conspicuous 

 among them, corals {Lithostrotion junceum the commonest as usual) 



(6 In a memorable account of the progress of the knowledge of the geo- 

 logy of the County, given by Mr. Topley at the Alnmouth and Alnwick 

 meeting of this Club, in 1879, and unfortimately not yet published. The 

 writer had given the thickness as " at least 8,000 feet " in 1878, a state- 

 ment much disputed at the time, and even now not always accepted. 

 See " Outlines of the Geology of Northumberland," p. 33. 



