120 PROCEEDINGS OF THE AMERICAN ACADEMY. 



that the substratum is crystallized. The central thesis of this paper 

 is that all vulcanism is a consequence of abyssal injection, or in other 

 words, that from the date of the oldest known pre-Cambrian lavas, 

 every volcanic vent has been opened because of a preliminary mechani- 

 cal intrusion of molten basalt into the acid earth-shell. 



Emphasis is laid on the absolute necessity of classifying the gases 

 and vapors which do important work at volcanic vents. These are 

 either magmatic or phreatic in origin. The magmatic volatile fluids 

 are subdivided into juvenile and " resurgent " ; the j^hreatic fluids into 

 vadme and connate. Each of these classes may be important in the 

 djiiamics of volcanic explosion ; on the other hand, the juvenile mag- 

 matic gases are assuredly the most important in keeping a volcanic 

 vent alive. 



Besides fissure eruptions and central eruptions, the writer recognizes 

 a class of vents not usually considered in treatises on vulcanism. This 

 third kind of volcanic action maybe caWed foundering e7'uptio?i ; the 

 hypothesis is presented that some batholiths have swallowed up parts 

 of their roofs, thus directly exposing a large area of each batholith to 

 the sky. 



This paper is chiefly concerned with the problem of central eruptions. 

 They are of two main classes. In the ^' jmncipal " class, each vent 

 represents emanations from a main abyssal injection ; in the other, 

 ^'^subordinate," class, each vent originates over a magmatic body (lac- 

 colith, sheet, etc.) which is satellitic with respect to a main abyssal 

 injection. Of these two classes, " principal " volcanoes must, on the 

 average, be the more intense in activity, of longer life, more productive 

 of lava-flows, and more clearly related to crustal fissures. The facts 

 of the field suggest that Kilauea is a " subordinate " volcano. Terti- 

 ary and Paleozoic examples are probably represented in Suabia and 

 Scotland. The localization of central vents and their very common 

 aligiunent are explained by the principle of abyssal injection. Lack 

 of alignment in a group of vents is suggestive of their " subordinate " 

 origin. In the nature of the case, " subordinate " vents must, in their 

 activities, show a high degree of independence of one another and of 

 neighboring " principal " vents. 



Continued eruption at a central vent is a heat problem. The pri- 

 mary heat of its abyssal injection is not the only source of thermal 

 supply. A leading place in the theory should be kept for the sujiply 

 due to chemical reactions among the primary constituents of the in- 

 jected magma. Abyssal injection means an enormous change in the 

 pressure conditions of the magma. As a result, the juvenile gases rise 

 toward the top of the magma chamber. They are concentrated in the 



