1849.] SHARPE ON THE SECONDARY ROCKS OF PORTUGAL. 135 



transported as ballast, but some are lying about, and a few remain 

 in situ. I have examined all of them, and find they are composed 

 of that variety of oohte which has been named Buckingham or Forest 

 Marble. Many of them are yellowish externally and bluish within, 

 owing probably to a difference in the degree of the oxidation of the iron 

 which has coloured them. The largest I have measured was about 

 3 feet by 4, very angular, being but little rounded ; while the smaller 

 ones, 30 inches by 20, whose corners had been modified and whose 

 sides had been smoothed, were covered with scratches and grooves. 

 Section of Railway Cutting at Buckingham. 



12 3 4 5 



1. Oclireous gravel, with boulders of forest 3. Dark claj', with Belemnites and rolled 



marble, and with Grypheese, Belemnites, fragments of chalk, 



and Ostreee. 4. Experimental shaft. 



2. Grey gravel. 5. Grey sand and gravel. 



The cutting (see fig.) is about fifty feet deep, and the boulders are 

 sprinkled among gravel, sand, and clay, about ten or twelve feet below 

 the surface ; and are not found lower down among the earlier deposits 

 of smaller pebbles, which must have come from all quarters, judging 

 from the variety of rocks they contain. Out of the latter I picked 

 the fragment of fossil bone I sent you a day or two ago — possibly a 

 portion of my old friend the Cetiosaurian, whose tail-bone I sent you 

 some years ago, and which you reported to the Society at the time'*'. 



I found one boulder only with perforations ; whether the work of 

 Pholades, or the impression of shells or wood, you will determine 

 from the specimen I send you, taken from one of the largest blocks, 

 and lying nearer the surface than any other. 



The country around here is very undulating ; scarcely two fields 

 have a similar aspect or inclination, and the hills are capped with 

 gravel, which makes it difficult to trace the stratification. The con- 

 tortions of the gravel beds are very curious, being in some places 

 almost vertical, and in others twisted like the letter S, according as 

 the bed is cut into obliquely or transversely. The gravel has been 

 penetrated to the depth of eighty feet near the pit you saw at Foscot, 

 in search of water, but without success. 



Looking at the boulders still in situ, I tried to make out from the 

 scratches from what direction they had come, but could not satisfy 

 myself on that point. 



2. On the Secondary District 0/ Portugal which lies on the North 

 of the Tagus. By Daniel Sharpe, Esq., F.G.S. 



General Sketch of Portugal. — So little is known of the geology of 

 Portugal that it may be interesting to give a general sketch of that 

 country before proceeding to the details of the district which is to 

 * Proceedings of the Geological Society, vol. ii. 1833-38, p. 190. 



L 2 



