Reports and Proceedings — Geological Society of London. 137 



The T^huelche Pebble-bed, which covers nearly the whole of 

 Patagonia, has been ascribed to marine action by some authors, by 

 others to glacial action, A third suggestion is the agency of big 

 rivers. No one of these agents alone could have produced the 

 observed phenomena ; the origin was complex. The bulk*of the 

 material was brought by glaciers from the Cordilleras to the sea, 

 which then covered the greater part of the pampas. As the sea 

 receded, it distributed the pebbles over the bottom, so forming 

 a continuous layer, such as now exists between the eastern coast 

 and the Falkland Islands. Torrents resulting from the melting of 

 the glaciers assisted in distributing the material from the Cordillera. 

 Part of the material on the present eastern coast was derived from 

 islets of quartz-porphyry in the Pleistocene sea. A great difficulty 

 is that no basalt-pebbles are found at Santa Cruz east of the flows. 



The drainage system includes several eastward-flowing rivers and 

 numerous lakes, some of which occupy transverse valleys cutting 

 through the Cordillera. An example of the latter is Lago Buenos 

 Aires. The history of this lake can be gathered from the evidence 

 observed on its shores. Lagos Musters and Colhuape are two other 

 interesting lakes near the eastern coast. Tlie width and depth 

 of the river- valleys are disproportionate to the present streams ; 

 this can be explained by a decreasing rainfall, and also by the 

 diversion of many tributaries to the Pacific. Some valleys are dry, 

 as, for example, the Great Caiiadon Salado. 



3. " On a Fossiliferous Band at the Top of the Lower Greensand 

 near Leighton Buzzard (Bedfordshire)." By George William 

 Lamplugh, Esq., F.G.S., and John Francis Walker, M.A., F.L.S., 

 F.G.S. 



This paper describes a newly discovered fossiliferous band at the 

 top of the Lower Greensand, overlain by the Gault, in the sand-pits 

 at Shenley Hill, near Leighton Buzzard, in Bedfordshire. The 

 fossils of this band present a different facies from that of any other 

 previously known fossiliferous horizon of the Lower Greensand, and 

 show closer afiinities with the fauna of the Upper Greensand than 

 have hitherto been recognized in any deposit below the Gault. The 

 Brachiopoda are closely allied to those contained in the Tourtia Beds 

 of Belgium. The fossiliferous bed is rather sharply marked off 

 from the underlying unfossiliferous ' silver-sands,' but is still more 

 sharply marked off from the overlying Gault. Stratigraphically it 

 forms part of the Lower Greensand, and cannot (without violence to 

 the accepted classification of the deposits) be considered to belong 

 to the Gault. The fossils constitute the newest Lower Cretaceous 

 fauna as yet recognized in Eugland. Several species, hitherto sup- 

 posed to be confined to the Selboi-nian, are now shown to have been 

 in existence before the deposition of the Gault. The lithological 

 characters of the bed indicate a sea-bottom of moderate depth, swept 

 by powerful currents, and the conditions were thus similar to those 

 which persisted in the neighbourhood throughout Lower Greensand 

 times. The overlying Gault shows a change to more tranquil waters, 

 probably of greater depth. 



