126 Mr. D. Sharpe on the Geology of 



thick, rises from the beach to the height of twenty feet ; and a few hundred yards farther two smaller 

 basaltic dykes rise in a similar manner. The basalt can be seen only on the beach, as the dykes run in- 

 land, and are entirely covered by the red sandstones belonging to the upper division of that formation, 

 constituting the cliffs with the adjacent country, and containing the sulphureous and lignite beds before 

 described. The disturbance produced by the basalt is so great, that eleven considerable faults occur in 

 the cliff within half a mile ; and to the same cause must be attributed the greater dip of the strata of 

 red sandstone in this district than to the westward of Cascaes. The line of elevation which begins at 

 Cascaes Bay runs north-east to the steep ridge of hills already mentioned between Canessas and Loures, 

 so that all the red sandstone between Cascaes and Loures is thrown up in the same direction, dipping 

 to the S.E. From this it may be concluded, that the whole of that range of hills was elevated by one 

 basaltic eruption ; and although we cannot trace the basalt below the surface along the line, still, as it 

 has burst through the strata at one extremity and upheaved them at the other, the whole must be 

 attributed to one cause, and the dykes at Cascaes considered to belong to the same period as the basalt 

 of the great eruption near Loures. 



BetAveen Loures and San Estevao das Gales a mass of basalt caps a hill of Hip- 

 purite limestone, the beds of which dip both from the north and south sides of the 

 hill toward the centre. This is the only spot where such an irregularity is met 

 with, and it may have been caused by a small eruption of basalt through the centre 

 of the hill. In any case, the cap is of the same epoch as the basalt already de- 

 scribed. 



On the beach to the west of Cezimbra, some masses of basalt have been intruded 

 between the beds of red sandstone, and may perhaps be of the same age as the 

 above. They have greatly disturbed the strata of sandstone, but the form of the 

 coast does not admit of the effects being well shown in a section. This is the only 

 spot south of the Tagus, where I met with basalt. 



To return to the north of the Tagus. Many hills of red sandstone to the north 

 of the great eruption are capped with detached masses of basalt ; several of which 

 are marked upon the map, but there are probably many others. At Sobral and 

 San Sebastiao are two very large masses, and there are some near Chilleiros and 

 Areas north of Cintra (Sect. 2 and 6). In all these cases, the basalt rests upon 

 undisturbed beds of sandstone, and there is nothing to lead to the supposition, that 

 the hills were the vents of eruption ; still it would not be safe to consider the cap- 

 pings as parts of the great sheet of basalt around Loures, and their origin and date 

 must be left uncertain. One mass, about three miles N.W. of Cintra, and near 

 Fontanellas, deserves separate mention. It appears to be of an older date than 

 the red sandstone ; and though there is no section showing the junction of the two 

 rocks, yet, as far as I could observe, the beds of sandstone rest horizontally upon 

 the basalt, which is of a more porphyritic character than is usual in this district. 



Although I had innumerable opportunities of examining the junction of the sub- 

 jacent rocks with the basalt, which rests in different places upon nearly every bed 



