444 SCIENCE PROGRESS. 



"gres de Silves ". North of the Tagus these sandstones 

 form the eastern border of the Mesozoic area, stretching in 

 a narrow band from Aveiro nearly to the town of Thomar. 

 South of the Tagus the " gres de Silves " is met with at Sao 

 Thiago de Cacem, at Carrapateira (N. of Cape St. Vincent), 

 and again as a narrow band resting upon the Palaeozoic 

 rocks in the littoral region of the province of Algarve (9). 



North of the Tagus the sandstones begin to alternate in 

 the upper part of the series with dolomitic and argillaceous 

 limestones, and these in turn are surmounted by dolomites 

 without sandstone belonging to the Sinemurien (40). In 

 the lower or sandy part of the series there are several beds 

 which contain remains of plants. These have been exa- 

 mined by both Heer (23) and Saporta (40) and seem to 

 indicate a Rhaetic or Infraliassic aore. 



The calcareous beds which occur higher up in the series 

 are called the " beds of Pereiros ". They often contain 

 marine fossils, for the most part gastropods and lamelli- 

 branchs, which are believed by Choffat to belong to 

 the Infralias. 



In Algarve the general succession is very similar. The 

 red sandstones of the lower part of the series have yielded 

 no fossils. The dolomites of the upper part contain marine 

 forms ; and as in the north, the dolomites gradually increase 

 at the expense of the sandstones. They are overlaid by 

 marls, spotted with white, which often contain gypsum, but 

 no fossils (9). 



Jurassic. — Jurassic rocks are found in four separate areas, 

 all of which are in the neighbourhood of the coast-line. 

 They extend, with some interruptions, from Aveiro in the 

 north of Portugal, to Cintra. They occur also in the 

 Serra da Arrabida, which forms the promontory south of 

 the Tagus which we call Cape Espichel. They are found 

 in the next important Cape to the south, the Cabo de Sines ; 

 and lastly, they are extensively developed along the coast 

 of the province of Algarve. 



The system is divided by the Portuguese geologists 

 into three stages, corresponding with the three divisions 

 adopted in Central Europe and named in ascending order,, 



