﻿148 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 5, 



gradually descending from it, and continuing in a true transverse 

 section to the S.S.E. across the lower hills, further inland, other strata 

 of finely micaceous, greywacke flagstones continue to dip in the same 

 direction, but at the lesser angle of about 45°. Then comes another 

 quartzose pebble and conglomerate bed of no great thickness, fol- 

 lowed by a greenish coarse-grained sandstone. The next overlying 

 strata are dark flagstones with a bluish or purple coloured exterior 

 and containing minute fragments of fossils. These beds are, it seemed 

 to me, a part of the orthoceratite and graptolite division (1), of which 

 hereafter ; for in an undulating and moory country like this, where the 

 strata are only visible at intervals, it would be unsafe to estimate 

 exactly the ascending series if we had not other proofs. In advancing 

 to Tor Mitchel, where a very large mass of limestone is quarried 

 and exposed on the right bank of the Assell stream, we found, how- 

 ever, an intermediate range of sandstone and pebbly conglomerate, 

 exposed at the farm of Birbals, with a dip reversed to the N.N.W. ; 

 and when, in making afterwards a section on the adjacent coast, I 

 there found the conglomerates of Kennedy's Pass also dipping to the 

 N.N.W. , I drew the inference that the deposits were arranged in a 

 trough, of which the black schists and flagstones (1) form the upper 

 or central part*. Here, then, we were manifestly approaching an- 

 other line of dislocation, of which we had the proofs on reaching the 

 limestone of Tor Mitchel. The physical evidence clearly indicates 

 that this limestone is on a line of axial disturbance, and is older than 

 any stratum described in the Saugh Hill section. The chief mass 

 of this rock is of dark grey colour with white veins, and is cut into 

 for a depth of about fifty feet, but it is so amorphous and isolated, 

 that it shows few clear relations to the before-named strata, except 

 that it seems to rise out from beneath them. At its eastern extre- 

 mity, however, bedding sets on, and a small nodular structure, very 

 much like that of many well-known Silurian rocks, becomes appa- 

 rent ; the whole decidedly plunging S. and by E. Again, the other 

 bank of the Assell brook is seen to be also made up of a portion of 

 this limestone, which is there both thin-bedded and concretionary, 

 and which, striking from E.N.E. to W.S.W., dips unequivocally to the 

 S.S.E. under massive undulations of schists, conglomerates, &c. &c. 



The Tor Mitchel limestone marks therefore a third axial line, along 

 which the limestone is traceable to the E.N.E., whilst to the W.S.W. 

 the upheaval is connected with the protrusion of great eruptive masses 

 of rock, of which hereafter ; and I have no doubt that this limestone 

 is of the same age as the fossiliferous rocks of Craig Head, and of 

 limestones on the more southern parallels, at Aldeans, Bogang, and 

 Craig Neil, which from their imbedded remains, as well as from their 

 position, are considered to be the oldest fossiliferous rocks of the 

 region. (See Map.) 



* Mr. J. Carrick Moore has informed me since these pages were written, that 

 he also found the strata, including pebbly beds and impure limestone, reversed 

 with a northerly dip on the hill-road from Girvan to Barr ; and he is of the same 

 opinion as myself, that the orthoceratite flags lie in a trough, as represented in 

 figs. 2 and 3. 



