FOREIGN CORRESPONDENCE. 



253 



and Doomairali. The island of Dissee, formed of a great number of 

 gentle prominences, composed of nearly vertical beds of gneiss, mica- 

 schists and other like rocks, sometimes impregnated with granite, is 

 highly interesting ; and M. Courbon's description of it and the 

 neighbouring shore will well repay perusal. 

 M. Courbon thus describes Perim : — 



" Perim is the result of a volcanic eruption below water. The lavas 

 and other erupted matter have first of all raised the coral bed, which 

 formed the bottom of the sea, leaving in its substance some of their 

 remains, and have then forced a passage to appear above the sea- 

 level. This volcano, of which the vast crater corresponded to the 

 whole bay of Perim, has been some time in activity ; and has covered 

 the island with mud, cinders, scoriae, puzzuoloni and, lastly, with the 

 trachytic rocks, which now cover its surface. 



" The volcanic action then ceased, and the calcareous sandstones 

 formed : at length a gentle upheaval elevated them, in their turn, 

 above the water ; and the island has since that time presented the 

 same appearance that it now does." 



The facts collected by M. Courbon, taken in conjunction with those 

 of his predecessors, prove that the Red Sea, which forms one of the most 

 marked localities on the surface of the globe, and of which the eastern 

 side in particular is aligned with a wonderful precision on the great 

 primitive circle of Thuringerwald, which passes Aden, bears traces 

 throughout all its length of eruptive phenomena of immense ex- 

 tent, and of an age certainly not very remote from the present epoch. 



On the Age of Fossil Bones, as determined by their composition. 



M. Delesse has furnished a paper on this subject, from which we 

 extract the following remarks : — 



" When animals are buried their fleshy parts soon decay, whilst 

 the hard part, which forms the skeleton, resists decomposition. 

 Nevertheless, the latter undergoes some alterations that are easily 

 discoverable in comparing the same parts of the skeleton of fossil, 

 with living animals. If one considers particularly the bones, their 

 alterations are shown by the changes in their density and their chemical 

 composition. First of all, it is very easy to prove that in fossil bones 

 their density always augments with age. This augmentation is very 

 sensible, not only in the bones belonging to different geologic epochs, 

 but also those of the present time. In the bones of a man, more par- 

 ticularly, it rises sometimes thirty-four per cent. It is generally higher 

 in the tusks of elephants and mastodons than in their bones. This 

 arises from the destruction of the organic matter or bony substance, 

 and also from the introduction of new mineral substances. 



" When fossil bones are impregnated with oxyde of iron, or pyrites, 

 their density rises very rapidly, and is only limited by the density of 

 those minerals. It is difficult to compare the carbonate of lime in a 

 noimal and fossil bone ; for it varies not only in each bone, but also 

 in each animal 



