the Neighbourhood of Lisbon. 1 1 7 



Sphmrulites ventricosa, Des Moulins. 



cylindracea ? Des Moulins. 



cristata „ 



The last three species are found in the chalk in the South of France. 



Also a very remarkable shell belonging to the family of Rudistes, which is, I believe, undescribed ; 

 ao-reeing in form with Diceras, having one valve spiral and the other curved ; but perforated longitu- 

 dinally by parallel pores, reaching the whole length of the shell, and open towards the junction of the 

 valves. 



2. Red Sandstone Formation. (PI. XIV. and PL XV. Sect. 1 to 4 and 6 to 13.) 



Below the Hippurite limestone is a very extensive series of deposits consisting 

 principally of ferruginous sandstone, but containing also beds of sand, marl, and 

 limestone. The following is the usual order of the strata : 



Sandstones, alternating with sand, the whole very ferruginous. 

 Marls of various colours, alternating with sand. 

 Sandstones, alternating with sand. 



Calcareous sandstones and coarse limestones, alternating with sand and sandstones, and occasionally 

 with marl. 



Coarse sands, sandstones, and coarse gritstones. 



The whole series divides naturally into three parts : 



1. Ferruginous sandstones and coloured marls. 



2. The calcareous division. 



3. Gritstones, &c. 



The different divisions pass so gradually into one another, that I have not at- 

 tempted to separate them into formations. 



The extent of country occupied by this series of strata is very considerable, but 

 it would be tedious to describe its boundaries in detail, and they may be better 

 seen on the map. The principal deposit reaches from Alhandra, on the Tagus, to 

 the coast north of Colares, and occupies nearly the whole country northward of that 

 line to Leiria, far beyond the range of country described in this paper ; but in that 

 district, it is partly concealed by the overlying Hippurite limestone, forming the 

 hills which range north-west from Villa Franca. In the portion more immediately 

 under consideration, the sandstones of the upper division occur along the southern 

 edge of the deposit from Bucellas to the Atlantic; the central calcareous beds may 

 be traced from Alhandra to Ericeira, passing the two villages of Enxarra and Mafra ; 

 and the grits and coarse sandstones of the lower division lie further north, about 

 Sobral, San Sebastiao, and Torres Vedras. The usual strike of the beds is from 

 E.N.E. to W.S.W., and the prevailing dip is to the S.E. ; but the whole country 

 is so cut up by innumerable faults, that beds may be found dipping in every direc- 

 tion and at every angle : this is particularly the case about Mafra. 



A very considerable fault, extending westward from Alhandra, has modified the 



