Beports and Proceedings. 471 



Eepoet of the Committee appoi2S"ted to Investigate the Alum 

 Bat Leaf-bed. 



By "W". Stephen Mitchell, LL.B., F.G.S., Caius College, Cambridge. . 



The bed known to geologists as the " Leaf-bed," or " Pipe clay- 

 bed," of Alum Bay, is the band of white clay which occurs in the 

 lower Bagshot beds, in Alum Bay, about 200 feet from their base. 

 It is about six feet thick, but one portion only, a few inches in thick- 

 ness, contains the plant remains. No other organic remains what- 

 ever have been noticed. 



The occurrence of these plant-remains was first observed by the 

 G-eological Survey in 1853. 



Dr. P. de la Harpe, of Lausanne, examined these, and gave a 

 notice of several species in a paper on the " Flora tertiaire de 

 I'Aiigleterre/' which appeared in the " Bulletin de la Societe 

 Vaudoise des Sciences Naturelles " for June, 1856. In Dec. 1860, 

 in conjunction with Mr, J. W. Salter, F.G.S., he prepared the list 

 which is published in the memoir of the Geological Survey of the 

 Isle of Wight. 



This list hicludes the collections from " the same strata worked at 

 Bournemouth and Corfe Castle, in Purbeck, Dorset ; " yet for the 

 compilation of it the total number of specimens that could then be 

 brought together from the three localities was but about 300. 



It is therefore no matter of surprise that in larger collections since 

 made many fresh form are met with. 



I went down to Alum Bay last September with Mr. Keeping, and 

 remained there during the working to note the appearance of the 

 leaves when first turned up. 



In tbe majority of instances, not only tbe outline, but the venation, 

 even the most delicate, is at first clearly visible, though a few hours' 

 exposure to the air almost obliterates the more delicate marks. A 

 washing with a solution of isinglass often preserves them, indeed in 

 some instances it brings them out even more sharply, but unfor- 

 tunately it often fails. There are some specimens on which I j^artly 

 traced the venation with pencil as soon as they were exposed. Now, 

 after an interval of ten months they are so faded that the part not 

 pencilled is hardly, if at all, to be made out. It is much to be 

 regretted that there is a difficulty in preserving the specimens, and 

 we shall be very glad to receive suggestions for their treatment. All 

 our specimens have had the usual isinglass wash, though I fancy it 

 somewhat obscures the character of the surface of the leaves. I can- 

 not speak with certainty on this point, for, as I had not anticipated 

 such a result, I did not record the character of the surfaces among the 

 notes I made on the spot. Still, from comparing the recollection I 

 bave of the appearance of the leaves when first tra-ned up with their 

 appearance now, I am almost certain this is the case. This I tbe 

 more regret as the character of the surface of the leaf is often a use- 

 ful help in determining its genus. I hope to have an opportunity of 

 again esamining this bed, and I shall endeavour to take both draw- 



