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



The Limits of the Pleistocene Lake of Portugal. 



In dealing with this question I liave to be guided by the Geological 

 Map of Portugal, on which is represented the area of the " Lacustre 

 superior " beds by a light-yellowish tint. Thus guided, the margin 

 of the lake stretched along the banks of the Taa;us from Cartaxo to 

 Abrantes ; then turning southwards it stretched to Alvallade, and 

 thence to the Atlantic coast atul the mouth of the Tagus. Over 

 this area the lacustrine beds rest directly on the granitic rocks, 

 or on the supposed "Lower Lacustrine" beds (Lacustre inferior), 

 the Miocene beds being absent ; they have therefore no connection 

 with the upper lacustrine deposits with which we are dealing. The 

 margin of these deposits is, according to the map, much indented 

 along the river-valleys flowing towards the west, and showing that 

 they have been considerably denuded during the rising of the land 

 which took place subsequently, and to which is owing the drainage 

 of tlie lake itself. 



During the period of depression in which the waters of the lake 

 accumulated, it would appear that the general level of its bed was 

 nearly that of the outer sea, and that the sea-waters gained access 

 occasionally during the earlier stage of its formation, owing to 

 which (as already stated) some marine molluscs gained access. 

 The magnificent harbour of Lisbon doubtless formed a portion of 

 the lake, and the narrow channel by which it is connected with the 

 ocean may be regarded as the unsubrnerged portion of the great 

 sub-oceanic caiion which carried the waters for about fifty miles 

 beyond its present outlet. On the final uprise of the land to its 

 present level the channel of the river was deepened, and the waters 

 of the lake were drained oflf ; and thus the great river which filled 

 the basin afterwards became the agent by which it was ultimately 

 drained. 



Such appears to have been the physical changes coming down 

 into recent times which have brought about the present conditions 

 of land and sea in the western part of the Iberian Peninsula. 



Glacial Conditions in Pliocene Times in Portugal. 



In connection with the Pliocene elevation here postulated, it is 

 interesting to observe that it was concurrent with extensive glacial 

 conditions in the western portion of the Iberian Peninsula. It has 

 long been known that the glaciers of the Pyrenees, like those of the 

 Alps, extended far beyond their present limits in the Glacial period, 

 but it is not so generally known that Portugal was the seat of 

 extensive glacial conditions. This, however, was the case; and 

 according to the views of Sgr. Delgado, the Director of the 

 Portuguese Geological Survey, than whom there is no higher 

 authority, these conditions commenced with the Pliocene epoch, 

 gradually giving way to one of progressive refrigeration of the 

 climate, accompanied by an invasion of glacial ice descending from 

 the mountain chain of the Serra d'Estrella. This chain, commencing 



