232 ANNUAL OF SCIENTIFIC DISCOVERY. 



the fossil mollusca. The author, however, rejects entirely the hypoth- 

 esis of an ice period, and is very severe on its supporters. 



One curious feet with respect to the present climate of Iceland is, 

 that it is, in most years, the opposite of that of the European conti- 

 nent. While the winter of 1844-45 was remarkably long and severe 

 in Europe, it was in Iceland unusually mild. The summer of 1845 

 was fine and dry in Iceland, rainy and cold in central Europe. Great 

 inconstancy of weather is characteristic of the climate, and a calm 

 tranquil air is the greatest of rarities, while storms of terrific violence 

 are very frequent. The author mentions one in which a companion 

 of his was blown off his horse, and the wind, in sweeping over the 

 fiord, raised clouds of spray that reached them at a height of 2,000 

 feet above the water. 



VOLCANOES NO SAFETY-VALVES. 



AT the meeting of the American Association, August, 1849, a paper 

 on the " Isolation of Volcanic Action in the Sandwich Islands, or Volca- 

 noes no Safety-Valves," was read by Professor James D. Dana. The 

 observations presented were made during the cruise of the Exploring 

 Expedition under Captain Wilkes, and have an important bearing upon 

 the theory of volcanic action. 



The island of Hawaii has an area of about 38,000 square miles, 

 and contains three lofty volcanic cones, or domes. The principal one 

 is Mount Loa, occupying the southern portion of the island, and be- 

 ing, according to the observations of Captain Wilkes, about 14,000 

 feet high. It has at its summit a large pit-like crater, somewhat 

 elliptical in shape, with its diameters 13,000 and 8,000 feet, and a 

 depth of 784 feet. There are no thin walls around it, as about Vesu- 

 vius; it is like a vast excavation in the wide summit-plain. Through 

 fissures in the bottom of the pit, vapors are constantly rising, and at 

 times the action is intense, and eruptions take place. 



Besides the summit-crater of Mount Loa, there is also a still larger 

 one, Kilauea, situated on the southeastern slopes of Mount Loa, 

 about 4,000 feet above the level of the sea. It is an amphitheatre of 

 rock, 7i miles in circuit, and 3^ in longest diameter, with a depth of 

 1,000 feet, large enough, in fact, to hold 400 such structures as St. 

 Peter's at Rome. The bottom plane is 2^ miles long and averages 

 of a mile in width. In the ordinary state of the volcano all seems re- 

 markably quiet. When visited by Mr. Dana, six months after the 

 eruption in 1840, there were wreaths of vapor rising from a few parts 

 of its inside surface, and in three places the red-hot lavas were in 

 constant ebullition. One of these lakes of lava measured 1,000 by 

 1,500 feet in its diameters. Over its surface jets were constantly 

 playing, precisely like jets over a boiling caldron of water ; yet 

 larger in the viscid fluid, for they rose to a height of 40 to 60 feet. 

 At other times Kilauea is in full ignition throughout the larger part of 

 its vast interior; the caldrons are more numerous and extensive, and 

 there are many spouting cones accompanied with detonations. These 



