Frof. E. Eull — The Great Pleistocene Lake of Portugal. 109 



at Garda, ranges in a south-west direction through the centre of 

 Portugal, attaining a height of 6,539 feet, and was, in all probability, 

 the most important axis of glacial dispersion during the post- 

 Pliocene period. Of the great extent of glacier-ice both to the 

 north of the Serra, where it invaded the affluents of the Mondego, 

 as well as the regions to the south towards the valley of the Tagus, 

 there can be no doubt since the publication of M. Delgado's 

 elaborate memoir,^ following on that of his late colleague, 

 M. Frederico A. de Vasconcellos,- both beautifully illustrated by 

 photographic plates, recalling all the familiar phenomena of 

 mountainous regions from which the glaciers have disappeared. 

 According to Delgado there were two glacial stages separated by 

 an interglacial one ("La phase interglaciaire "), corresponding to 

 those which, in company with some British geologists, I have long 

 held as having occurred in the British Isles. The most important 

 point to be noticed is the occurrence of these glacial phenomena 

 at an epoch corresponding to that of the elevation of the land and 

 the erosion of the now submerged valley of the Tagus. If there 

 are any geologists who regard this concurrence of events as 

 accidental I am unable to agree with them. To the mind of myself, 

 and a goodly number of other physicists both in Britain and 

 America,^ the glacial conditions are the direct result of the land 

 elevation, for the simple reason that altitude above the sea-level 

 is the governing factor, though not the only one, in the occurrence 

 of warm and cold temperatures in all parts of the globe, even in 

 equatorial regions. If the surface of Portugal was sufficiently 

 elevated to allow of the erosion of the Tagus out to a distance from 

 the coast of 55 miles, and to a depth of over 7,000 feet from the 

 surface of the ocean,* we have the measure of the elevation of 

 the land at the Glacial period. Adding, therefore, the depth of the 

 submerged canon (7,200 feet) to the present elevation of the Serra 

 d'Estrella (6,539 feet), we have as the result a mountain 13,739 feet 

 high, a height sufficient, notwithstanding its latitude, to give rise 

 to a system of glacial dispersion and erosion, to some degree, 

 comparable with that of the Alps at the present day. I now feel 

 satisfied that, on observing the forms of the granite masses as they 

 emerged from beneath the lacustrine gravels towards the Portuguese 

 frontier, I was not mistaken in recognising them as ice- worn surfaces. 



1 " Note sur I'Existence d'anciens Glaciers dans la Vallee du Mondego," par 

 J. F. Nery Delgado, extr. des Communicadoes da Direc. dos Tratalhos Geologicos, 

 tomeiii (1895). 



2 Ibid., tome i, p. 189 (1887). 



^ See Professor J. "W. Spencer on " Professor Hull's Sub-oceanic Terraces, etc.," 

 a review, American Geologist, vol. sxxv (March, 1905). 

 * Trans. Vict. Inst., vol. xxxi, p. 284, footnote. 



