282 Correspondence — D. Bahillie. 



lateral extension of the Permian. Associated with the breccias are 

 other proofs of thrusting: (1) thrust or shear-planes; (2) disturbed 

 and displaced masses of Lower Limestone; (3) intruded breccias; 



(4) slickensided and grooved, horizontal and vertical surfaces ; 



(5) cleavage ; (6) folding, both on a local and on a general scale; 

 (7) buckling, thickening, and squeezing- out of beds ; (8) phacoidai 

 and other structures ; and (9) Assuring. The main thrust at Marsden 

 appeal's to have acted from a few degrees south of east to a few 

 degrees north of west ; there are, however, distinct evidences of 

 movement from other directions in different parts of the district. 

 Experiments made on the compressive strength of the rocks affected 

 by the thrust at Marsden indicate that the thrusting reached 

 a maximum of about 300 tons per square foot. Observations made by 

 Mr. S. E. Haselhurst, M.Sc, in the Cullercoats area seem to prove 

 that the thrusting occurred later than the post-Permian movement of 

 the Ninety Fathom Dyke — some faulting in the area is, however, 

 later than the thrusting — and it appears evident that the shattering 

 of the strata was produced prior to the Pre-Glacial era of denudation. 

 It may have been connected with the Miocene movements that 

 produced such marked changes in the physiography of Britain. 



COERESPOUIDEITCE. 



THE LIMESTONE FRAGMENTS IN THE AGGLOMERATE OF THE 

 "ROCK AND SPINDLE" VOLCANIC VENT, ST. ANDREWS, FIFE. 

 Sib., — Since the publication of my note under the above-named title 

 (see Geol. Mag., May, p. 201) I have to record the further observation 

 of a very remarkable fact. During a recent visit to the "Rock and 

 Spindle " my friend Mr. R. M. Craig, M.A., B.Sc, of the Geological 

 Department, St. Andrews University, and myself found that certain 

 large masses of rock which, stand almost vertically in the seaward 

 extension of the agglomerate, and which we had long been accustomed 

 to regard as consisting merely of hardened sandstone — they weather 

 curiously like some of the siliceous sandstones along the shore — were 

 in reality portions of a seam of limestone which must have measured 

 at least 12 feet in thickness. These contain very large crinoid stems, 

 isolated cup corals, polyzoa, etc., and look exactly as if they belonged 

 to some of the beds at the base of the Carboniferous Limestones as 

 exposed on the coast at Pittenweem. Certainly they can scarcely 

 have come from the Calciferous Sandstones, and would accordingly 

 appear to afford the strongest confirmation of the above opinion based 

 almost solely on the palaeontology of the fragments at the upper part 

 of the beach. 



David Balsillie. 



DREIKANTER. 

 Sot, — The reviewer to whom Mr. Grabham objects (Geol. Mag., 

 May, 1911, p. 239) seems in his review (Geol. Mag., Feb., p. 85) to 

 describe the words ' dreikanter ', ' zeugen ', etc., as ' technical terms \ 



