1849.] SHARPE ON THE SECONDARY ROCKS OF PORTUGAL. 139 



line of demarcation between these two great systems is as strongly 

 marked in Portugal as it is in our own country. 



On the south of the tertiary basin, the centre of the province of 

 Alemtejo is covered by secondary beds, probably older than those to 

 be described on the north of the Tagus, but the true age of which 

 has not yet been determined : these are bounded on the south by the 

 lofty chain of hills, called the Serra de Monchique and Serra de 

 Caldeirao, which separate Alemtejo from Algarve, and which consist 

 of schists and slates, with the exception of granite at the Cabe9a de 

 Monchique. Dr. Welwitsch has informed me that schists also occur 

 along the coast of Alemtejo from Cape Serdao to Sines, and that the 

 Cape of Sines is formed of syenite. 



On the south of the chain of Monchique and Caldeirao lies the 

 little kingdom of Algarve, which has been carefully surveyed by 

 M. Bonnet, from whom we may hope to receive a geological descrip- 

 tion of it ; that gentleman told me that a band of secondary rocks 

 lies on the south flank of the schistose chain, which is again overlaid 

 along the south coast by tertiary deposits. Considerable outbursts 

 of trap near Cape St. Vincent are mentioned by Link. 



Thus it appears that there are two districts of secondary and ter- 

 tiary rocks in Portugal ; the southern of which consists of the narrow 

 strip of Algarve ; the other commencing on the north side of the 

 Algarve mountains extends up to the Vouga, forming a narrow triangle 

 of which the base at the south is about forty miles long, and the 

 height from north to south is about 200 miles : the secondary rocks 

 of this latter area are divided into two parts by the tertiary basin of 

 the Tagus and Sado. It is the northern division of this secondary 

 district, viz. that which lies to the north of the Tagus (see fig. 1), 

 which I now propose to describe. 



Throughout this paper I shall commence with the upper formations, 

 and describe them in descending order under the following heads : — 



Hippurite limestone, equivalent to our chalk. 



Subcretaceous series. 



Jurassic series. 



Sandstones of undetermined age. 



With the exception of certain deposits of sandstone last mentioned, 

 no secondary rocks older than the lias have been seen in Portugal 

 north of the Tagus ; nor have any traces of the carboniferous series 

 been met with in any part of Portugal. 



Hippurite Limestone ; equivalent to the Chalk of the North of 

 Europe. 



The description of this formation will be found in my paper on the 

 * Geology of the Neighbourhood of Lisbon,' p. 115; and as this rock 

 does not occur to the north of the district described in that memoir, 

 I have little to add to the account there given of it. 



The hippurite limestone is the uppermost of the secondary de- 

 posits, and near Lisbon is usually overlaid by basalt, which bursts 

 out in great quantities in that neighbourhood in the interval between 



