the Neighbourhood of Lisbon. 115 



deposition of any of the tertiary strata, and contributed by its degradation to form 

 the earUer tertiary deposit. 



The description of the basalt will be given in that part of the paper which relates 

 to the igneous rocks. 



Secondary Formations. 



This class of deposits consists of, 1. Hippurite limestone. 2. Red sandstone. 

 3. Espichel limestone. 4. Slate-clay and shale. 5. San Pedro limestone ; and 

 6. Older Red conglomerate. 



1. Hippurite Limestone. (PI. XIV. and PI. XV. Sect. 1, 3, 6 to 8.) 

 The uppermost secondary formation consists of calcareous beds varying from 

 soft and argillaceous limestone to beautiful hard marble. I have called it the 

 Hippurite limestone, as some of the beds abound with fossils belonging to the 

 family of'Rudistes, and nearly related to the genus Hippurites. It usually rests 

 conformably upon the red sandstone. 



Hills composed of this limestone form a very important feature in the country 

 north and west of Lisbon, but I did not observe the formation south of the Tagus. 

 A very good section is exposed on both sides of the narrow valley of Alcantara, 

 close to Lisbon, where the following beds occur : — 



Soft argillaceous limestone, alternating with thin beds of marl 40 feet. 



Grey marl 6 — 



Rubbly argillaceous limestone, containing SphcBrulites 50 — 



Limestone, containing Sphcerulites and other shells belonging to the family of 



Rudistes 30 — 



Soft argillaceous limestone 20 — 



Hard, compact, white limestone, with numerous interstratified beds of flint .... 50 — 

 Beautiful, hard, compact, white limestone 100 — 



This list does not include the whole thickness of the formation. The cliffs be- 

 tween Fort St. Julian and Cascaes consist of alternations of marl and grey lime- 

 stone, the marl predominating in the upper, and the limestone in the lower part ; 

 and they are probably the highest beds of the formation. A good section of the 

 lowest beds is in a ravine through which the road from Tojal to Bucellas passes. 

 The limestone is there of a coarse texture and dark grey colour, with rather a 

 slaty fracture, and forms beds three or four feet thick, with thin partings of marl. 

 Putting these sections together, the formation will be found to exceed 500 feet. 



This limestone composes several distinct tracts ; the most northerly being a line 

 of bold hills extending from Cereal to Villa Franca, rather beyond the district which 

 I examined. Another narrow zone of Hippurite limestone ranges from Bucellas 

 westward to Pero Pinheiro ; resting to the north upon red sandstone, and having its 

 southern edge concealed by basalt. Only the lower beds are visible at Bucellas and 



q2 



