Geological Society. 31 S 



specimens of Terebratula intermedia, Perna rugosa, and Trigonia 

 literata. 



Of the formations below the red sandstone, the author offers no 

 data for estabhshing a comparison with deposits in other parts of 

 Europe further than that the Espichel and Arrabida limestones may 

 be of the same age as the limestone of the rock of Gibraltar, and 

 that the shale near Cintra may be the equivalent of the shale which 

 underlies the Gibraltar limestone, and constitutes a considerable 

 portion of Andalusia. He is also of opinion, that the Cintra shale 

 is of the same age with the immense deposit of similar composition, 

 which covers the centre of the province of Alentejo, extending from 

 Alcacer do Sol to the confines of Algarve. 



The older red conglomerate of the neighbourhood of St. Ubes, 

 Mr. Sharpe considers as probably identical with the conglomerate 

 largely developed on the banks of the Vonga, and which rest3 

 upon mica slate a little to the south of Oporto. 



IGNEOUS ROCKS. 



Basalt. The principal deposit of this rock forms one of the most 



important features in the geology of the district to the north and west 

 of Lisbon, occupying an irregular area, estimated to be not less than 

 eighty square miles. It is difficult to define its limits without reference 

 to an accurate map ; but it may be stated to form a tract of very 

 varying breadth, from the shore west of Belem by Queluz, and 

 Odivellas to Loures. In the neighbourhood of the last village, it 

 turns S.W. and N.E., ranging in the former direction to the 

 neighbourhood of Montelavar, and in the latter nearly to Verdelha 

 on the banks of the Tagus. Besides this immense continuous mass, 

 many of the hills north of Oeiras, near the mouth of the Tagus, are 

 capped by basalt, evidently outlying patches, once connected with 

 the o-reat deposit. Basalt also forms the summit of the hills near 

 Sobral and St. Sebastiano, resting upon the red sandstone. It has 

 been already stated, that beds of trap alternate regularly and with- 

 out any ajipearance of disturbance with the central division of the 

 shale formation near Cintra. 



The rock varies considerably in character, and is occasionally 

 columnar. It is stated to have frequently the appearance of a black 

 indurated clay with an irregular schistose cleavage, and breaking 

 into very irregular rhombs. 



The only beds which rest upon the basalt belong to the tertiary 

 series, but it overlies both the Hippurite limestone and the 

 red sandstone. To the westward of Loures, it cuts through these 

 formations; and the red sandstone, to the south of the line of 

 intersection, has been brought to a level with the Hippurite lime- 

 stone to the north of the line. The strata of Hippurite limestone 

 to the north are nearly horizontal, while those of the red sandstone, 

 and limestone to the south, are highly inclined. Hence Mr. Sharpe 

 infers that the great mass of basalt was poured forth from fissures 

 in the neighbourhood of Loures. 



The cliffs in the bay of Cascaes exhibit fine sections of basaltic 

 dykes and disturbances ; and on the beach west of Cezimbra masses 

 of basalt are intruded into strata of red sandstone, which exhibit 



