194 Dr. Clarke's Account of [March, 



68 West of the Alleghanys, in Louisiana. Four years. Dunbar. 

 Transatlantic climate. 



53 Madeira. Heberden. Climate of islands. St. Croix, of 

 Teneriffe, 71-4°. The remainder of the island of Teneriffe, in 

 the plains, 61-2°. Buch. 



54 Old observations of Tartebout. They appear good. Bag- 

 dat, lat. 33° 19'; according to Beauchamps, 73'8°. The four 

 seasons, 50-8°, 74-6°, 92*6°, 77°; but there was reflection 

 from a house. The thermometer falls to 29 , 8". Under the 

 equator, at 3,000 feet high ; mean temperature, 71 -2°. 



55 The calculations are made from the observations of Nouet 

 (Decade, ii. 213). The following are the mean temperatures of 

 the 12 months: 58-1°, 56-2°, 64-6°, 77-9°, 78-4°, 83-6°, 85-1°, 

 85-8°, 79-2°, 72-2°, 63°, 68-6°. (Neibuhr, 72-2.) Temperature 

 of Joseph's Well, 72-5°. Catacombs of Thebes, 81-4°. Well of 

 the great pyramid surrounded by sand, 88*2°. Jomard. Bas- 

 sora, on the Persian Gulf; mean temperature, 77-9°; winter, 

 64°; summer, 90-8°; July, 93-2°. 



56 Orta. Humboldt. Nouv. Esp. iv. 516. Jamaica, coast. 

 80-6°. Blagden. 



" Ferrer, 1810— 1812. Con. des Terns. 1817, p. 338. Wells 

 of 10 feet deep; air, 76°; water, 74-4°; in 1812, maximum, 

 Aug. 14, 86°; minimum, Feb. 20, 61-6°. Grottos, 81-5°. Hum- 

 boldt, Observ. Astron. i. 134. 



68 Humboldt. Pondieherry, 85-1°; Madras, 80-4" ; Manilla. 

 78-2° ; Isle de France, coast, 80-4°. 



Article VI. 



Account of some remarkable Minerals recently brought to tfm 

 Country from the Island of Jean Mayen, in the Greenland 

 Seas, North Latitude 7 1°. Also a Description and Analysis 

 of a Substance called Petalite, from Sweden. By Edward 

 Daniel Clarke, LL.D. Professor of Mineralogy in the Univer- 

 sity of Cambridge, &c. In a Letter to the Editors. 



GENTLEMEN, 



Twenty years ago, being engaged in a voyage among the 

 western islands of Scotland, 1 had an opportunity of examining 

 the very singular appearances exhibited by the prismatic rocks 

 of Canna. The shores of that island are covered with a jet- 

 black shining sand, which, owing to the partial notions I had then 

 formed, and to prejudices imbibed by a residence among the 

 volcanoes of the south of Italy, I supposed to be volcanic. Pro- 

 bably that arenaceous appearance had been derived from basalt, 

 or trap. I have often, however, since regretted, that I did not 



