160 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



strata appear to follow conformably (see aw ^e p. 1 58, and section No. 3, 

 fig. 4) . It might therefore be thought that we had here the regular 

 succession of the beds above the Jurassic limestone of Val d'Ovos, yet 

 I can hardly believe this to be the case, because the limestone beds at 

 Val d'Ovos are of less thickness than in many other parts of the 

 chain, and their series may therefore be incomplete ; and it is probable 

 that if the Thomar beds were of an age immediately following on the 

 Jurassic limestone, they would more often be seen in connection with 

 them. 



On the other hand, I cannot connect the Thomar limestone with 

 the subcretaceous series, since I have seen no fossils in it, and it differs 

 in mineral character from all the subcretaceous limestones observed 

 to the westward ; and the sands below it have no peculiar character 

 which can guide us in determining their age. We must therefore 

 leave the determination of the age of these beds until more information 

 is collected about them. 



Limestone and Sandstone of Coimbra. 



The city of Coimbra stands on a limestone formation of great thick- 

 ness, which rises unconformably from below the beds of limestone and 

 sandstone of the subcretaceous period, as previously described (p. 146), 

 and shown in sections, Nos. 1 and 2 (figs. 2 & 3). 



The upper beds of limestone are well seen at Fornos, three or four 

 miles north of Coimbra, and again two or three miles to the south of 

 the town on the Lisbon road ; they consist of thin alternating beds 

 of hard argillaceous limestone and marl. From below these rises a 

 hard, compact, grey limestone of great thickness, dipping N.W. 30° 

 to 45°, on which the town is built, and which extends for several miles 

 on both sides of the river to the N.E. and S.E., forming nearly a 

 semicircle. Organic remains must be rare, as I found no trace of 

 them in several spots which I examined ; but in the Museum of the 

 University of Coimbra are a few Ammonites from the upper beds of 

 the limestone at Fornos, which led me to suppose on a very slight ex- 

 amination that the limestone belongs to the upper or middle part of 

 the oolitic series. 



At the upper part of Coimbra the limestone is seen to rest con- 

 formably on a formation of ferruginous sandstone of very great thick- 

 ness : the beds at the junction dip N.W. 30°. 



The following is the order of the beds of the sandstone formation : — 



1. Hard calcareous conglomerate lying below the Coimbra lime- 

 stone ; of little thickness. 



2 . Softer ferruginous sandstonewith some beds of redand blue marls. 



3. Ferruginous sands. 



4. Ferruginous sandstone, containing numerous large blocks of in- 

 durated slate, jasper, &c. 



Each of the three lower divisions is of great thickness, and the 

 whole covers a breadth of about four miles, with a dip usually of 

 N.W. 30°. The sandstone rests at Portella, four miles east of Coimbra, 

 against a lofty ridge of micaceous schist which runs nearly north and 

 south, and forms the eastern boundary of the secondary district. 



