14 On Terrestrial or Epigeic Deposits 



ground, and the indestructibility of the rock which forms their 

 narrow circumference ; but to us the greater number appear- 

 ed to be the result of a sinking down of a more recent epoch. 

 Among the latter, we shall cite those which we frequently meet 

 with in the Peninsula of Hermionia from the massive trachytes 

 of Poros to the island of Hydra and Cranidi. They are seen 

 at the summit and the sides of the mountains, and, what in my 

 opinion proves their recent origin, in the midst even of the allu- 

 vions of the enclosed basin of Didymus. We find, at a quarter 

 of an hour's journey to the north-west of that village, situated 

 at the deepest part of the basin, and near the opening of its 

 gulf, a circular cavity with vertical walls, the depth of which 

 is from 20 to 25 metres, and the diameter from 200 to 300. 

 The walls merely present pebbly alluvium, in which it is im- 

 possible to detect any difference from the base to the summit, 

 as that occurs in basins without outlets, which have not been 

 exposed to denudations. We are of opinion, that the whole of 

 the cavities of Herniconia may be the result of volcanic phe- 

 nomena, of which this country has been the theatre since the 

 appearance of the trachytes ; and, that the more general causes 

 of the phenomenon, are the action of subterraneous rivers and 

 waters of infiltration, in the middle of broken up and moveable 

 beds of the green-sand of the lower part, and the sinking of the 

 vaults of the caverns, whose existence we have demonstrated. 



Ochremis earth c^f limestone mountains. — After the melting 

 of snow, there are formed in lacos, situated on the most elevated 

 mountains, little lakes, which the heat and the fissui'cs in the 

 rocks soon drain ; in that case, there is nothing but the ochreous 

 earth, of which we have spoken without having as yet investi- 

 gated its origin. On again finding this substance on the highest 

 and most isolated peaks on the surface of the soil, and in the 

 fissures of the rock, but only in limestone mountains, we have 

 frequently asked what could be its origin. We believe we have 

 discovered that this earth is identical with the cement of the 

 osseous breccias, and with the matrix of the pisolitic iron of 

 our Jura table-lands ; but this comparison would require to be 

 made with greater care. It dissolves with effervescence in acids, 

 and leaves, besides the hydrate of iron, a residue of silica in 

 small impalpable grains, with some little crystals of quartz, and 



