418 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 22, 



it appears certain they must both have existed under similar circum- 

 stances ; hence it would appear injudicious to come to conclusions 

 with regard to physical conditions from the examination of a single 

 set of remains. 



In the preparation of this paper I hare been assisted by the loan 

 of specimens by my friend the Rev. P. B. Brodie, who is heartily 

 thanked for this and other assistance ; also by Mr. W. Binfield of 

 Cheltenham, whose cabmet is rich in fossils from the lower lias lime- 

 stones. 



May 22, 1850. 

 The Hon. George Stephens Gough was elected a Fellow. 

 The following communications were read : — 



1 . On a Gap in the Greywacke Formation of the Eastern Lam- 

 MERMUiRS filled by Old Red Sandstone Conglomerate. 

 By William Stevenson, Esq. 



[Communicated by Sir R. I. Murchison, V.P.G.S.] 



The occurrence of yast masses of conglomerate on both sides of the 

 Lammermuir chain has been well known to geologists since the days 

 of Hutton and Hall. It appears, however, never to have been sus- 

 pected that the formations of the north and south sides were con- 

 nected by a band of considerable breadth running completely across 

 the chain from Doon Hill, about two miles from Dunbar, to the 

 Hardens Hills, about the same distance west from Dunse. 



The position, extent, and relations to the adjoining strata of this 

 interesting formation of conglomerate will be best understood by re- 

 ference to the accompam"ing sketch (see Map). 



The whole district occupied by the greywacke, conglomerate, and 

 trap rocks is almost uniformly hilly, the height of the hiUs ranging 

 from about 800 to 1400 feet above sea-level, those composed of con- 

 glomerate being in general fully as high as those consisting of grey- 

 wacke or igneous rocks. The tracts occupied by the strata of the old 

 red sandstone and lower carboniferous formations are much lower and 

 flatter, and generally rise no higher than 300 or 400 feet above the 

 level of the sea. 



The conglomerate occupies a trough in the greywacke, evidently 

 the result of an ancient dislocation of great extent. AX the margins 

 it is seen overlapping the upturned ends of the greywacke strata, 

 which are generally either vertical, or dip at angles of 4.5° or upwards, 

 to about W.N.W., the dip being rather steeper on the east side of 

 the conglomerate than on the west. The thickness of the mass of 

 conglomerate towards its central parts cannot be readily ascertained, 

 as the deepest rapines do not expose its base. In Shippith Glen it is 

 seen to be several hundred feet thick ; but even here there are no 

 symptoms of the underhdng grewacke. In regard to composition, 

 it is pretty uniform, consisting chiefly of waterworn masses of grey- 

 wacke, together with a few of speckled porphyry, and occasionally a 



