A very remarkable kind of mineralized wood is found on the mountain of Drapuhlid in Iceland. In external ap pearance, it cannot be distinguished from a mass of char coal ; yet it is very heavy. Chalcedony is observed in some specimens fillirig small fissures. When the carbo naceous matter is burned, a mass remains, which, when bruised, divides into fibres finer than hair, and resemhling asbestos ; shelving that the silicious matter had penetrated into the most minute pOres of the wood. This substance occurs in a bed of tuf lying under pearl stone. This last substance occurs of a light grey colour, and also dark green approaching to pitch stone. It was found also form ing the principal ingredient in a variety of tuf not before described. " It is composed chiefly of masses of black pearlstone, imbedded in a dull blackish green matrix. It contains also masses of amygdaloid, and we found a few nodules of pyrites in it, coated with pitch coal. Pitchstone occurs at Houls, and on the west side of the mountain called Baula.
The surturbrandt of Iceland has not been seen in situ by a mineralogist. It has a great resemblance to black oak found in lakes and rivers in many countries. But though capable of being shaped into tables and other articles of furniture, it is not in a condition to be cut by a plane into shavings, being somewhat brittle.
For a description of the individual minerals which occur in these regions, we must refer to the 7th volume of the Edinburgh Transactions, and to Sir George Mackenzie's Travels. The silicious depositions of the Geysers and other hot springs are very interesting, but are now well known to mineralogists.
The volcanic formation of Iceland is perhaps the most extensive in the world, covering an extent of at least 60,000 square miles. Sir George Mackenzie distinguishes three formations, which are ascribed to the action of in ternal heat. The oldest is that already described as sub marine lavas, which resemble trap rocks more nearly, both in position and structure, than any other ; and which he supposes to have flowed at the bottom of the seas.
The next is a class of lavas to which he has given the name cavernous, from its containing numerous cavities, some of them very extensive. This is supposed to be form ed of rocks which hare been subjected to subterraneous heat, but not removed from their original place. Many of the appearances presented by this class seem to warrant this conclusion in regard to its mode of formation ; but the conjecture is thrown out merely to attract the attention of future observers of volcanic countries. The last is the ordinary erupted lava, including ejected substances. Per haps there is no field in which the investigation of the op erations of heat could be carried on with greater facility than in Iceland, the rocks are so well exposed to view. But the shortness of the season in which travelling is prac ticable presents a strong obstacle. Yet we hope that some able mineralogists will repeat and extend the obser vations made by Sir George Mackenzie, and avail them selves of the information afforded by that gentleman.
We understand that the celebrated traveller and mine ralogist, Baron Von Buch, has carefully examined the Ice landic collection in the cabinet of the Royal Society of Edin burgh, and has the intention of soon communicating to the public the result of his examination of various volcanic. countries.
See Letters on Iceland, by Von Troil; Voyage en Islande, fait par crdre de sa Majeste Danois, par M M. Paulsen et OlafseiL ; Hooker's Tour in Iceland, 1809 ; Tarvels in Ice land, 1810, by Sir G S. Mackenzie ; Transactions of the Royal Society of Edinburgh, vols iii. ar,d vim. See the article VOLCANO, which Baron Von Buch has promised tO write for this work.