33S PROCEEDINGS OF THE AMERICAN ACADEMY 



that the crevices of the lavas, in the vicinity of the crater 

 of Vesuvius, emitted sulphur fumes ; the iiapkiu containing 

 eggs, while being cooked, was coated with sulphur. 



Dr. Pickering remarked, that, so far as his observations ex- 

 tended, sulphur vapors were abundant in lava crevices, wher- 

 ever vapor was emitted. Referring to the great lava lake of 

 the volcano of Hawaii, he said there was no perceptible smell 

 of sulphur near its surface. 



The President, Dr. Peters, and Professor Horsford also took 

 part in the discussion. 



The President expressed an interest in the question of the 

 origin of volcanic ashes, referring to the fact of their being 

 carried by winds and dispersed over extended areas at the time 

 of eruptions ; falling on vessels at sea far from any land. 



In answer to an inquiry from the President as to the nature 

 of volcanic ashes, Dr. Hayes replied, that they are the finely 

 divided parts of broken down volcanic aggregates, having 

 generally the composition of silicates of alumina, slightly con- 

 taminated by other silicates. To have a clear view of the 

 origin of these ashes, it is necessary to consider that volcanic 

 action, under its differing intensities, either fuses together or 

 merely compacts assemblages of divers minerals, including sul- 

 phur compounds of metals and of earths. This action is often 

 aqueous or hot-water action, and the rocks formed include tlie 

 elements of their own destruction, on exposure subsequently to 

 the air and moisture. Thus one of the most solid is the true 

 Augitic Trachyte, which will not resist exposure to a New 

 England atmosphere one year, without crumbling and disin- 

 tegrating. Craters of elevation are composed in large part of 

 this rock, often covered by true fused lavas in part. The latter, 

 at the points near their source, are tolerably compact, but as 

 they pass along the surface, they become tumefied and scoria- 

 ceous, and hence subject to decomposition. When the sul- 

 phurets have been engaged in the trachytes, decomposition 

 commences soon after exposure to humidity, attended by the 

 emission of vapors and acid fumes, which corrode and decom- 



