1865.] BRYCE BEDS BENEATH BOULDER-CLAY. 213 



the present paper (see p. 219). Beds very similar to it occur in the 

 valley of the Aar, above the great gorge, and on the low south-west 

 shores of the Lake of Brientz. In regard to the origin of the Upper 

 Drifts there are many formidable diiSculties. They are most pro- 

 bably due to disturbances attendant on the re-elevation of the land, 

 and may have been partly formed out of the waste of the Boulder- 

 clay by the action of glaciers which had become local as the ice was 

 disappearing, and partly by the action of rivers, necessarily, under 

 the supposed conditions, larger than now. The resemblance, indeed, 

 to a river deposit is in many places remarkable. As shell-beds are 

 not found among these Drifts in Arran, we need not here speculate 

 in regard to a second subsidence. Shells of recent British species 

 are indeed found in the caves of the cliff which marks the old sea-line, 

 and on the terrace at its base, as Professor Eamsaj' long ago showed ; 

 but these are much below the level of the Upper Drifts. This 

 terrace, which around the Arran shores has an elevation of 25 feet, 

 is carved out upon Drift-beds and. rocks alike ; it was once a sea-bottom, 

 most probably after the close of the Glacial period ; its elevation 

 marks the last change which affected the island, and gave to Arran 

 its present maritime border and the inland cliff which forms a 

 singularly picturesque feature in its coast-scenery. 



3. On the OccTJRRENCE of Beds in tlie "West of Scotland beneath the 

 EouLDER-cLAY. Bj James Bryoe, M.A., LL.D., F.G.S. 



An examination of the Drift-beds in the island of Arran, undertaken 

 last summer with the view of determining their true sequence, led 

 me to the conclusion that the lowest bed there — the lower Till or 

 true Boulder-clay — did not contain any fossils. Having noticed, 

 while conducting the inquiry, how many difficulties and causes of 

 error are met with, which an observer does not encounter in the 

 case of rocky strata, I began to doubt the accuracy of the statements 

 so often put forward that fossils occur in this bed, and to consider 

 that the supposed cases which are on record might be explained in 

 various ways. Other drifts with boulders, thoiigh superior in position, 

 may readily be mistaken for the Boulder-clay. The upper surface 

 of this last-named bed undulates violently; and shells in part of the 

 overlying Arctic-shell bed, occupying a hollow in the undulation, 

 might seem to be in the older deposit, especially if, as in Arran, the 

 laminated clay, which usually in Clydesdale divides the Boulder-clay 

 from the shell-bed, happened to be absent, — the observer being, of 

 course, supposed to overlook the undulation. And, further, the wash 

 or facing, formed over the whole surface of a drift-section by atmo- 

 spheric causes and runlets of water, might contain shelly fragments 

 from the bed above, which, adhering to the surface merely, would 

 yet appear to be in the Boulder-clay. There was yet another expla- 

 nation. It was possible that fossils said to be deep in the Bo\ilder-clay 

 might really be in beds beneath it, of diifcrcnt mineral structure, 



