1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



soutliward. In process of time that sea-bottom, tlius formed to a 

 great depth of clay, sand, gravel and boulders, was elevated to the 

 surface, level or unequal according as the elevating force acted with 

 uniform or variable intensity, and formed the land of Central Russia. 

 The incoherent materials, after a long period of repose in the new- 

 formed land, are again subjected to atmospheric agency, broken into 

 smaller fragments or worn down into impalpable mud, to be suspended 

 in water and floated to the mouth of the Volga, or to settle at the 

 bottom of the Caspian in a stratified deposit. There they form anew 

 ground on which moUusca live, whose shells will become buried in the 

 slowly forming stone ; and this stone covering a region where we know 

 internal heat to be active, may become metamorphic, and assume a com- 

 pact or crystalline structure. Thus the same matter which was once 

 a constituent of a granite in the Alps of Scandinavia, after undergoing 

 numberless changes in form and structure, through an incalculable 

 period of time, changes however identical with those which we now see 

 in progress, may be hereafter raised up in Asia as the elements of a 

 schistose rock ; in like manner as our oldest sedimentary strata must 

 have been derived from the disintegration of pre-existent granites, or 

 other forms of unstratified rock, of which the land was then composed. 



You may probably recollect having read, in the newspapers of the 

 autumn of 1845, an account of a quantity of dust having fallen from 

 the atmosphere on the Orkney Islands ; it was also said to have fallen 

 to the thickness of an inch on ships in that part of the North Sea. 

 It was supposed to indicate a volcanic eruption of ashes in Iceland ; 

 and the conjecture was proved to be correct ; for, on the 2nd of Sep- 

 tember of that year, the great volcanic mountain of Hecla, after a re- 

 pose of nearly 80 years, again burst forth. On the same day, a quantity 

 of dust fell on a Danish ship in lat. 61° N., and longitude 7° 58' W. 

 of Greenwich. It blew at the time strong from the N.W. by W. 

 From this point Hecla is 533 miles distant. 



We learn from the work of Mr. Ebenezer Henderson*, that between 

 the years 1004, the earliest record, and 1768 inclusive, there had been 

 23 eruptions, the intervals varying from 6 to 76 years. Sir W. 

 Hooker in his work on Iceland, writing in 1810, says that the last 

 eruption of lava was in 1 7QQ, and that it lasted from the 15th of April 

 to the 7th of September, but that flames unattended with lava ap- 

 peared in 1771 and 1772, since which period neither fire nor smoke 

 had appeared. Sir George Mackenzie, however, describing his ascent 

 of Hecla in 1810, states that on removing some of the slags at the 

 summit, those below were too hot to be handled, and on placing a ther- 

 mometer among them it rose to 144°f . 



Since the eruption in 1845, the island has been visited by French 

 and German geologists, and we shall no doubt receive ere long a de- 

 tailed account of their observations. On the 26th of October last, M. 

 Dufrenoy laid before the Academy of Sciences at Paris a letter he 

 had received from M. Descloizeaux, who in company with M. Bunsen 

 had visited Hecla last summer. He mentions a change in the height 

 * Journal of a Residence in Iceland. f Travels, p. 248. 



