Prof. E. Hull — The Great Pleistocene Lake of Portugal. 107 



of these river- valleys, and owing to which, there was no deposition 

 of strata under the ocean. To this cause I venture to attribute the 

 absence of representatives of the Pliocene formation in Portugal y 

 as, indeed, is the case with other parts of the Continent and the 

 western areas of the British Isles. 



From the above considerations it will be seen that between the 

 "Upper Tertiary Sands" of Sharpe (or the "Lacustre superior" of 

 the Geological Survey) and the marine "Almada Beds" there is 

 no physical connection. As regards periods of formation, they are 

 separated by the whole of the Pliocene and probably post-Pliocene 

 periods, as already stated. It is therefore necessary to revise the 

 classification of the post-Cretaceous series of the authors above 

 quoted, and I therefore venture to substitute for these the following 

 arrangement of the beds. 



Bevised Classification. 



Quaternary- 



Tertiary 



Cretaceous 



1. Eecent and Quaternary. 



h. 



3. 



Lacustrine. 



Post- Pliocene and Pliocene. 



4. Miocene. 



5. Eocene (?) 



6. Upper. 



Alluvia of the valley and estuary of 

 the Tagus. 



Marls vnth Zymncsa, sands and gravel. 



Not represented unless by some land- 

 glacial beds due to elevation. 



Alniada Beds, calcareous marls and 

 limestones with marine fossils. 



Unfossiliferous sands and gravels 

 (Lacustre inferior) of doubtful age, 



Hippurite Limestone. 



Fersonal. 



When observing the sections of strata, along the line of the 

 railway for several miles between Carlaxo and Abrantes, consisting 

 of white, yellow, and red laminated sands, with lines of rolled 

 pebbles, horizontally stratified, and extending to a height of 150 to 

 200 feet above the river, it became evident that these beds could 

 not have been deposited by the river itself; and I arrived at the 

 conclusion that they must have formed the bed of an extensive lake.^ 

 I was therefore anxious to ascertain whether my conclusion was 

 borne out by the Geological Survey Map of Portugal. It was 

 therefore with great satisfaction that on consulting the maps I found 

 that these beds were included under the term "Lacustre superior." 

 They are specially coloured, and, according to Sharpe, cover an 

 area of " 2,000 to 3,000 square miles." ^ On crossing the Tagu& 

 at Praia we find the country formed of extensive plains of gravel, 

 from which at Das Vargans and Cunheira the bed-rock of granite 

 emerges and the gravel and sand cease ; this limit of the lacustrine 

 beds probably corresponds very nearly with that of the original 

 waters of the lake itself. To this point of the limit of the lake it is 

 now necessary to direct our attention for a brief space. 



Supra cit., p. 138. 



