WORK OF PORTUGUESE GEOLOGICAL SURVEY. 447 



Choffat divides the system into the following subdivisions 

 (in ascending order) : — 



Infravalanginien. 



, Valanginien. 

 Hauterivien. 

 Urgonien. 

 Beds of Almargem. 

 Eellasien. 

 Cenomanian Limestone. 



Most of these subdivisions are the same as those adopted 

 in Southern France and bear the same names. The beds 

 of Almargem represent the Aptian, and possibly the Albian, 

 of northern geologists, while the Bellasien is in part, and 

 perhaps entirely of Cenomanian age. The " Cenomanian 

 Limestone " may possibly include the lowest part of the 

 Turonian ; but no higher beds of the Cretaceous are 

 known. 



The difficulties which have been encountered in the 

 examination and correlation of the Cretaceous deposits of 

 Portugal, were due to the rapid changes in lithological 

 character which the beds undergo even in a very short 

 distance. The result of this has been that different fades 

 of the same horizon have often been described as different 

 horizons. 



These rapid lateral changes were due without doubt to 

 the nearness of the Cretaceous coast-line. Even in the 

 Upper Jurassic, as we have already seen, transported 

 materials play a considerable part, and this is still more true 

 of the Cretaceous. Coarse sandstones and conglomerates 

 are here abundant. 



There are only two districts, namely, the region of 

 Cintra and Bellas and that of Eastern Algarve, where the 

 base of the Cretaceous is represented by marine beds, and 

 both these districts are near the present sea margin. Here 

 the whole of the Cretaceous excepting the beds of Almar- 

 gem consists of marly limestones with a marine fauna. 



In the Cintra area, for example, the beds from the In- 

 fravalanginien to the Urgonien, and the Bellasien also, con- 

 sist chiefly of marls and marly limestones. The beds of 



