GEOPHYSICAL LABORATORY. 177 



magma. The development of the new vent of Novarupta is ascribed to the 

 enlargement of a channel along one of the fissures. The later extrusion of the 

 stiff lava forming the dome of Novarupta is found to have been similar in many- 

 respects to that of the "spine" of Pel6e. 



At Falling Mountain the most interesting features are those resulting from 

 fumarolic action. E\ddence of a process of solution and transfer of rock ma- 

 terial in the gaseous medium was found here, and the results of similar pro- 

 cesses around the vents of the fumaroles in the valley were observable. It is 

 suggested that the properties of the evolved gases indicated by this selective 

 gaseous transfer may at times lead to results of great importance in volcanic 

 processes. 



A study has been made to determine the manner in which the top of Mount 

 Katmai disappeared and the great crater-pit was formed. It seems quite 

 certain that the material was not blown out directly, but must be accounted for 

 otherwise. Crater subsidence may have been a factor, but it is believed that 

 collapse of the crater-walls and incorporation of the material in the new 

 magma were chief features. It is recognized that the latter process demands a 

 large quantity of heat for its accomplishment, and the magma evidently was 

 not at very high temperature prior to extrusion ; therefore accessions of heat 

 seem to be demanded. A considerable problem is thus presented, but it 

 does not seem at all insuperable, and it is believed that the evidences of solu- 

 tion are so strong that they can not be disregarded. 



One of the important features of the eruption brings up for consideration a 

 phenomenon to whose significance little attention seems to have been paid 

 hitherto. It is that of a gas-charged magma gradually developing the explo- 

 sive condition after some interval has elapsed subsequent to its ascent from 

 the depths. The Katmai magma seems to have followed this course, and the 

 phenomenon is apparently not uncommon. This is beUeved to have great 

 significance and to imply changes of physical environment during its ascent, 

 effected with such rapidity that internal readjustments were not able to keep 

 pace with them. Many of the current theories of volcanism are based upon a 

 fundamentally different conception of the nature and properties of the magma. 

 It is thought that it may be advantageous in many cases to consider matters 

 from the new standpoint here suggested. 



In other matters, also, theories that have been proposed and somewhat 

 widely accepted are apparently not in accord with the evidence found here. 

 It has not been possible in this article to discuss these matters exhaustively, 

 and other matters of interest have not been touched upon. Fuller treatment 

 willbe presented in articles to follow. 



(32) American optical glass for American instruments. George W. Morey. Am. Pho- 

 tography, 14, 129-133 (1919). 



A popular account of the development of the American optical-glass 

 industry and of the manufacture of optical glass. 



