WORK OF PORTUGUESE GEOLOGICAL SURVEY. 449 



Tertiary. — Towards the close of the Cretaceous period 

 there appear to have been considerable outbursts of basalt, 

 which at their base are interstratified with marls containing- 

 a terrestrial fauna. They may, perhaps, be connected with 

 the great outflows of North-western Europe ; but they have 

 not yet been properly examined, and up to the present their 

 age remains uncertain. 



The Tertiary beds which occupy so much of the plain 

 of the Tagus and occur elsewhere in smaller patches have 

 not attracted much attention from the Portuguese geologists, 

 and little seems to have been written concerning them. 



The more recent deposits, however, have been the 

 subject of various papers (13, 33, 39, 43), and evidence 

 has been brought forward showing the existence of 

 prehistoric man (1, 10, 17, 34-37), and also, in the higher 

 mountains, of the previous presence of glaciers (20, 44). 

 Striated blocks and other evidences of glacial action have 

 been discovered in the Serra d'Estrella. 



" Tiphonic" valleys. — But perhaps the most interesting 

 problems in the whole of Portuguese geology are those 

 which concern the valleys called by Choffat " tiphonic ' : 

 (3, 6). These are met with chiefly in the Mesozoic area 

 North of the Tagus. In all cases there is a level floor 

 bounded on several sides by hills of Jurassic rocks. The 

 floor is formed of reddish marls, the " Marls of Dagorda," 

 and sometimes upon it rise low ridges of dolomite. Choffat 

 has shown that the dolomites contain fossils of the same 

 age as the Beds of Pereiros (Infralias), and he believes the 

 marls to belong to the same period. The marls appear 

 to clip below the Jurassic beds which form the hills surround- 

 ing the valleys ; but the lower beds of the Jurassic are 

 always absent. The appearance of a conformable sequence 

 is in fact merely deceptive and the valleys are bounded 

 by faults, the floor of the valley being raised so that the 

 Infralias of the floor abuts against the higher Jurassic beds 

 of the surrounding- hills. 



Connected with these tiphonic areas are considerable 

 outbursts of ophite and teschenite (3, 6, 30, 31), and 

 Choffat has brought forward some evidence to show that 



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