WORK OF PORTUGUESE GEOLOGICAL SURVEY. 445 



the Lias, Dogger, and Malm. There is, unfortunately, no 

 general account of the whole ; but Choffat has given us a 

 brief description of the Jurassic of Algarve (9), and a 

 fuller account of the Lias and Dogger (2) and of the lower 

 part of the Malm (12) north of Lisbon. 



The Lias and Dogger are almost entirely marine, and 

 correspond very closely with the contemporaneous beds 

 of Central Europe. Many of the northern zones have 

 been recognised in Portugal and further research no doubt 

 will reveal others. It may be noted here that Choffat 

 includes the Callovian in the Dogger (5, 8). 



The Malm, on the other hand, is a much less purely 

 marine formation, and in places contains beds of lignite, 

 which are sometimes, for example, at Cape Mondego, 

 extensive enough to be worked. It differs considerably 

 from that of Northern Europe, and is very variable in 

 character. Everywhere, however, it may be divided into 

 two stages, the Lusitanian below and the Neo-jurassic 

 above. 



North of the Tagus the Lusitanian as it exists in 

 the country of Torres Vedras has been described by 

 Choffat (12). This area includes the chain of Montejunto 

 and the low-lying country limited on the east by the 

 Tertiary basin of the Tagus and on the south by the 

 Cretaceous rocks of the neighbourhood of Lisbon. The 

 Lusitanian beds rest upon Callovian deposits with 

 Peltocems athleta and Cosmocerus calloviense ; and they 

 themselves consist chiefly of limestones in the lower part and 

 of clays with banks of sandstone in the upper. The lime- 

 stones contain various Ammonites, among them several 

 Oxfordian forms ; while in the clays are found numerous 

 gastropods and lamellibranchs, which are mostly similar 

 to those from the Sequanian or Astartian of the jura. 



Elsewhere, however, excepting in the eastern part of 

 Algarve, the Oxfordian fauna has not been discovered, and 

 the Sequanian rests directly upon the Callovian, but without 

 any visible unconformity. 



In the Montejunto country the passage between the 

 Lusitanian and the succeeding Neo-jurassic beds is formed 



