538 KEPORT— 1882. 



In the rather limited researches which the author has had opportunity to make 

 in respect to glacial phenomena in geology, he has felt interest in seeking for indi- 

 cations presented by the striated rock-faces themselves, which might conclusively 

 show in which way the ice must have advanced. He wishes, in the present paper, 

 to make mention of one or two rather remarkable indications of this kind which he 

 has met with in the last two years. 



At Skelmorlie, on the Frith of Clyde, at a height of about 150 or 200 feet 

 above the sea, he has found glacially striated surfaces, on red sandstone containing 

 pebbles of quartz and of other kinds of stone. Many of these pebbles projected 

 considerably out from the general smoothed and striated surface of the sandstone, 

 and from each of such peblsles there extended to one side a ridge of the sandstone, 

 like a tail, the sandstone being there worn away less than at other places devoid of 

 the protecting influence of any hard protuberant pebble. The manner in which tlie 

 protection had Ijeen given must have been this : — The ice, in passing over the 

 protuberant hard pebble, must, in virtue of its plasticity, have had a groove 

 moulded into it by the pebble, and this groove passing forward from the pebble in 

 the motion of the ice, must have worn away the sandstone facing to it less than 

 would the other parts of the ice-face wear away the sandstone facing to them. 

 The length of the noticeable tail would depend mainly on the distance that the ice 

 could advance before the groove in it would be gradually obliterated. A pebljle of 

 the size of a bean, for instance, might often be found to have a tail visible for a 

 length of five or six inches, or perhaps from that to a foot, and larger pebbles might 

 be seen to have tails two or three feet in length. 



Again, on the recent visit to the railway cuttings near Aberfoil, referred to by 

 the author in his previous communication, a remarkable example was found of a 

 glacially worn and finely striated conglomerate rock face. The situation of this is 

 at Ballanton, about a quarter of a mile from Aberfoil. The hard pebbles were of 

 various sizes, and many might be of sizes such as those of beans, and eggs, and 

 large potatoes. Some of them were worn away by the ice continuously with the 

 surrounding sandstone matrix ; but those of them which projected showed very 

 conspicuous tails, many of which might be four or five feet long or more. 



Various other indications, presented by the striated surfaces themselves, of the 

 direction along the striffi in wliich the motion of the ice has been made, may occa- 

 sionally be found. Doubtless none can b(3 more strikingly remarkable than the 

 tails extending from hard pebbles or other hard nodules, or hard veins, included in 

 the ice-worn rock. The author wishes, however, to mention that on making minute 

 examination, by a magnifying lens, of the scratches on worn quartz pebbles in the 

 striated sandstone at Skelmorlie, he was able to find also in these verj' small mark- 

 ings, indications wliicli appeared clearly to show the direction of the motion of the 

 ice, and that these indications were perfectly in agreement with Ihose given by the 

 tails extending from the pebbles along the striated sandstone surface. 



3. On the Equivalents in England of the ' Sahles de Bracheux,' and on the 

 southern limits of the Thanet Sands. By Professor Prestwich, F.B.S., 

 F.G.S. 



The author dwells on the importance of establishing, in adjacent but separate 

 basins, a certain number of well-defined horizons. The lignite and fresh-water 

 beds of the Paris Lower Tertiaries and of the Woolwich series form one such zone, 

 but he considers the generally accepted correlation of the beds beneath not satis- 

 factory. The Bracheux sands are still, by all other geologists, placed on the 

 level of the Thanet sands and of the Lower Landenian beds. Some years ago ' 

 the author saw reason to suppose they might rather be correlated with the lower 

 beds of the Woolwich series, and in this opinion he is confirmed by the more 

 recent researches of M. Deshayes, by whom many new species were described, and 

 many rectifications made of the species in M. Graves's lists from the Bracheux beds. 



' Quart. Jourii. Geol. Soc. for August 1855, p. 219. 



