39 
The red sandstone Mr. Sharpe considers to belong also to the 
secondary system, in consequence of his having obtained from it 
specimens of Terebratula intermedia, Perna rugosa, and Trigonia 
hiterata. 
Of the formations below the red sandstone, the author offers no 
data for establishing 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 rests 
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 that 
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, in 
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 great 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 appearance of disturbance with the central division of the 
shale formation near Cintra. 
The rock varies considerably in character, and is occasionally 
columnar. Itisstated 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 
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