:54 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



soutli, the watershed being east and west. The strata, in like 

 manner, take the same division, the northern portion being for the 

 most part composed of volcanic rocks, and the southern of primary 

 sedimentary deposits. Viewed at a distance, from the deck of the 

 steamer, when approaching Prinkipo from the west, the most casual 

 observer cannot but be struck with the great difference in the phy- 

 sical aspect of the two mountains ; for while the soft trachytic rocks 

 of San Cristo have been rounded into beautiful outlines by the action 

 of the atmosphere, the hard quartzose rocks of San George have 

 withstood the ravages of time, and stand out in rugged masses and 

 conical peaks. 



The strata are divided into: — (1) Volcanic or eruptive rocks, which 

 may be subdivided into Trachytic and Trappean ; and (2) Primary 

 sedimentary rocks. 



a. Tracliytic rocJcs. — Commencing from the extreme north-eastern 

 point of the island, at the village of Prinkipo, and passing along the 

 western side by the Ville de Giacomo and Morton's Floiu'-mill, and 

 thence beyond a little bay that lies south of the great promontory 

 that juts out from the mainland to the west, the strata are com- 

 posed of white trachytic rocks, of a feldspathic nature, in general 

 soft, forming sandstones in part, which are composed then of 

 siliceous crystals in a feldspathic paste, unstratified and jointed, 

 the joints being further cemented by the infiltration of iron in many 

 parts, colouring the face of the stone at the joints of a dark-red and 

 blackish colour. There are extensive quarries opened out on these 

 sandstones around the brow of the San Cristo Mountain, where 

 the strata can be well examined ; some of the quarries have a per- 

 pendicular face of from 40 to 50 feet ; and the stone works into 

 angular blocks, aftbrding a very ordinary but durable building-stone 

 of moderate hardness. 'No signs of stratification whatever are to be 

 observed in these rocks. In other parts, the trachytes are comjDosed 

 of a soft stone, or kaolin, which readily decomposes, wherever ex- 

 posed to the action of the atmosphere, into a very pure kaolin, 

 capable of being used largely in the manufacture of pottery- ware. 

 The joints being the harder substance in this latter rock, from the 

 iron cement, are less decomposed than the body of the stone, and 

 stand out in the sea- cliffs a complete system of network, of a dark- 

 red colour. 



In approaching the Primary strata the trachytes become more 

 siliceous, and alternate with beds of quartz rock. Here also much 

 brown iron ore has been deposited in the joints of the trachytic 

 rocks, rendering them in part metalliferous, and changing their 

 colour to a dark red. In the cliffs immediately to the north, a band 

 of these metalliferous trachytes is exposed for not less than 70 yards 

 in breadth, and most probably extends across the island at the line 

 of junction of the volcanic and sedimentary rocks, as the ferruginous 

 deposits are again met with on the north-eastern side, of w^ich I 

 shall have to speak presently. 



Eeturning again to the extreme north-eastern point of the island, 

 and going thence along the eastern coast, immediately after leaving 



