106 Prof. E. Hull— The Great Flektocene Lahe of Portugal. 



underlying " Almada Beds " in the neighbourhood of Lisbon is very 

 clearly shown in the sections accompanying Mr. Sharpe's paper ; 

 for, while the Ahnada Beds are inclined at angles varying from 

 10° to 15°, the Upper Sands are well-nigh horizontal. In addition 

 to this the Almada Beds have been faulted and denuded, and 

 subjected to disturbances which do not affect the Upper Lacustrine 

 Sands. All these phenomena go to indicate absolute disconnection 

 between the two formations, a disconnection which in time would 

 in other districts have been filled up by the Pliocene beds, but 

 which are here altogether absent from their place in the geological 

 series. The cause of this lacuna I hope to be able to explain 

 further on. 



The Suh- Oceanic Extension of the Tagus. 



"When a few years since I was endeavouring to determine by the 

 aid of the soundings on the Admiralty^ Charts the physical features 

 of the land areas now covered by the waters of the Eastern Atlantic, 

 I was enabled to show that the principal rivers of Western Europe, 

 and partly of Africa, were continued across the continental platform 

 to great depths and various distances under the ocean from their 

 present outlets. Amongst these the sub-oceanic Tagus was one of 

 the best developed, and can be well delineated owing to the large 

 number of soundinos off the coast of Portuo;al. The isobathic 

 contours are perfectly clear, as will be seen from the photographic 

 slides, together with those of the Adour in the north of Spain and 

 the Congo on the coast of Africa.' In reference to the sub-oceanic 

 caiion of the Adour, I may mention that Dr. Nansen, who in 

 northern latitudes has studied these physical features, has stated 

 that it is impossible to suppose that it can be anything else than 

 a drowned river valley.- 



1 do not intend to go farther into the question of these submerged 

 valleys, except as they are connected with the geological history of 

 the Tagus valley. Their existence is clearly due to river erosion, 

 inasmuch as they could not have been formed under the ocean- 

 waters themselves. The question we are here concerned with is 

 the determination of the geological period of their formation. The 

 conditions must have been those of great land elevation affecting 

 the ocean-bed and adjoining lands. That they are not of great 

 geological antiquity is shown by the fact that the rivers with 

 which they were continuous are geologically modern, more modern 

 indeed than the Chalk, and, in this district, than the Miocene, 

 "which, as shown above, is a marine deposit. 



Pliocene Elevation. 



It is to the Pliocene and post-Pliocene epochs that we must therefore 

 refer that great land-uprise which would be necessary for the erosion 



^ These photographic pictures were then exhibited, but have ah'eady been described 

 in the Trans. Viet. Inst., vols, xxxi and xxxii. ^~'-^ 



2 Nansen, " Bathymetrical Features of the North Polar Seas, etc.," p. 95 

 (1893-5). 



