THE GfeOLOGlSl'. 



lire glaciers in latitude 50 clegs, north. The Snowdon group is at 

 least three degrees further north than this, and, if instead of being- 

 part of an island, that district, at a higher elevation, were part of a 

 broad continent spreading east and west, we should have in its peaks 

 and valleys all the conditions needful for the formation of large 

 glaciers ; and the same may be said of other mountain regions of 

 the British Islands." 



I now send you these speculations for what they are worth, 

 although in the long run I think it will appear that the wide-spread- 

 ing, long-continued, and most intense cold of the glacial period was 

 due to some unexplained cause far more general than any mere 

 changes in physical geography. 



BRITISH ASSOCIATION MEETING. 



ON A NEW POINT IN THE STRUCTURE OF SIGILLARIA, WITH SOME 

 REMARKS ON THE BIVALVES OF THE COAL. 



By J. W. Salteb, Esq., F.G.S. 



Among the very fine collections of fossil-plants in the Manchester Museum, 

 are some specimens of Sigillaria well worthy attention, and which show, as I 

 believe, a new point of structure, bearing on their aquatic habits. 



They belong to that section of the genus which is distinguished by the leaf- 

 scars, being arranged close together in the vertical rows, not at a distance apart, 

 as in most of the species. So close, indeed, that they press on one another, and 

 compel each other to take an hexagonal form. 



At certain points along the trunk, new lines of scars are interpolated, so as 

 to make the number of ridges greater (and at the same time the individual 

 ridges narrower) in the younger portions of the tree. In Favulttria these 

 intercalations very much at particular spots, forming a sort of varix, or 

 node, not very obscurely marked. At these points, too, in certain species, the 

 stem is swelled, the spaces between the ridges deepened — the ridges themselves 

 narrower and more prominent, and altogether angular in form. Brongniart's 

 artist lias badly represented such a varicose swelling in his figure of Sigillaria 

 hexaaona. 



Tne species in which I have observed this characteristic arc : — the Favidaria 

 tessellata, from Tonge, Bolton ; F. nodosa, from Oldham, and a species from 

 Glamorganshire ; F. hexagona, from Manchester coal-field. 



In a perfectly preserved stem of F. tessellata, from the roof of the "four- 

 foot" coal, the intervals between the ridges are occupied by rows of circular 

 scars, not hexagonal, nor purse-shaped, as the leaf-scars between them are, but 

 round. Nor with the characteristic flattened surface and double imprint from 

 which the vascular bundles of the leaf arise, but deeply indented, and with a 

 minute protuberance in the centre, which structure is characteriseic of the 

 rootlets of the underground portion of the stem (Stigmaria). 



The look of these small interpolated scars is so different from those of th 

 leaf-rows (they are clearly not interpolated ridges, for they die out at each 



