266 



THE GEOLOGIST. 



the author in his former communication showed them to have had at the 

 period of the high-leyel gravels, that is at from 100 to 200 feet above the 

 floors of the present valleys, the difference of level then of the upper de- 

 posits of Loess to be accounted for will be diminished to 100 or 150 feet, 



— a difference still considerable ; but, 

 on the other hand, these extremes are 

 not always attained. At all events, 

 this brings the whole of the Loess 

 within the possible range of inunda- 

 tions of the old Pleistocene rivers at 

 different periods according to their 

 age ; the higher beds having been de- 

 posited by the overflowings in the 

 earliest periods and before the exca- 

 vation of the present river-valleys, 

 the lower beds after the present val- 

 leys had been formed, but while the 

 old meteorological conditions still prevailed. These deposits of Loess thus 

 furnish a measure of the volume of water anciently brought down by the 

 rivers during floods, and show how very far they exceeded their present 

 representatives, and how great must have been their erosive action. Flood- 

 deposits will always consist of shingle in the river channels ; sand in 

 sheltered places ; fine silt over the area where the flood waters repose. 

 In this manner the author considers the high- and low-level gravels and 

 the Loess of all the levels to have been formed. 



This flood-origin of the Loess being admitted, it follows that as that de- 

 posit is found at 50 to 100 feet above the highest beds of gravel, the floods 

 of these periods must have risen like those of the Arctic regions, but to 

 even a greater extent (50 to 100 feet), above their summer levels. The 

 fluviatile shells found in the gravels and Loess were stated to be identical. 



Geological Society of London.— J^^n'Z 16, 1862. — 1. " On the 

 Position of the Pteraspis-beds, and on the Sequence of the Strata of the 

 Old Eed Sandstone Series, in South Perthshire/' By Professor E,. Hark- 

 ness, F.R.S., P.G.S. 



At the Bridge-of-AUan the lowest beds seen of the Old Eed Series are 

 (1) conglomerates of trap-rocks, overlaid b}^ (2) grey sandstone passing up- 

 wards into red sandstone. These grey sandstones have afforded to Mr. 

 Powrie a Fteraspis (perhaps P. rostratus), and fragments of Cephalaspis 

 have also been found in them. Next above come (8) purple shales (at 

 Craig Arnhall) ; then the brown sandstones (4) of Downe Castle ; and 

 lastly at Laurick, grey sandstones (5) again. These all have a N.W. dip, 

 as seen along the Teith. From about Laurick to Callander the strata are 

 best seen in the Keltic burn. They have a S.E. dip, and form the other, 

 but steeper, side of a S3^nclinal trough (about twelve miles wide) ; and 

 liere grey sandstone (5), (4) brown sandstone (at Bracklin Linns), (3) 

 purple shale. (2) red and grey sandstone, and lastly (1) a conglomerate 

 (here composed of felstone) present an analogous succession to that be- 

 tween Laurick and the Bridge-of- Allan. At Callander the conglomerate 

 lies almost vertically against the metamorphic Lower Silurian rocks of the 

 Grampians, trap-rock intervening. The author estimates that the Old 

 Eed strata have a thickness of 7000 feet. 



".^^'^ ^^]'^ Western Extremity of the London Basin ; on the Westerly 

 Tliiumng of the Lower Eocene Beds in that Basin; and on the Grey- 

 woihcrs." By AViUiam Whitaker, Esq., B.A., F.G.S., of the Geol. Surv. 

 Crreat Britain. 



b b' b" Loess ; d a high-level gravel ; 

 e c' low-level gravels ; m, n, o, the levels 

 to wliich the river rose during inundations 

 at different periods. 



