DALY. — THE NATURE OF VOLCANIC ACTION. 109 



The importance of this fact is manifold. Its recognition aids in our 

 understanding: the short Hfe of many volcanoes of the central t3'pe ; 

 the lack of lava flows at many of them ; the independent activity of 

 neighboring vents ; the chemical dissimilarity of the lavas from neigh- 

 boring vents ; the quite common clustering of many small vents in a 

 region which shows no trace, or but few traces, of the alignment of its 

 volcanoes ; and the frequent evidence of surface deformation in such 

 regions. The evidences for this type of vulcanism are indirect, but 

 they are numerous ; taken together, they form a combination of no 

 mean strength. 



In the first place, an excellent analogy to the vents from satellitic 

 injections can be observed in nature. The blow-holes and driblet cones 

 formed on the surface of the deep lava flows of Etna, Reunion, Hawaii, 

 Savaii, etc., are continued in their brief activity because of the thermo- 

 gaseous energy of lava quite removed from the parent vent. The blow- 

 holes occasionally opened in the dome-shaped "bulges" or "tumuli " 

 formed on the pahoehoe of Hawaii or Reunion are particularly instruc- 

 tive, for such tumuli, when just formed, represent small laccoliths of 

 still fluid lava capped by recently frozen lava-crust. 



To the weight of analogy is to be added that of a priori reasoning. 

 According to almost any of the extant theories of igneous action, vul- 

 canism originating in magmatic satellites should be expected. Many 

 satellitic injections of great size have been exposed by erosion ; it would 

 be a matter for distinct surprise if none of them ever perforated its 

 roof. 



Field observation must naturally make the compelling test of the 

 principle. Have we any active example ? Can we find traces of it in 

 denuded regions where erosion enables us to study the anatomy of vol- 

 canoes 1 Each method of applying the field test has its own difiiculty. 

 In the first case the satellitic injection is inaccessible and can only be 

 located through inference ; in the second case it is but rarely that de- 

 nudation could expose the injected mass without destroying the conduit 

 above. Yet the writer believes that the field inferences seem to support 

 the principle. 



The case of Kilauea, as an illustration, will be presented in some 

 detail ; the conception was first clearly attained by the writer during 

 his field-work at that volcano in 1 ;»()!). 



Kihiuea, the Vent of a Stitellitir Injection. — A glance at the govern- 

 ment map of the island of Hawaii shows the reader that the contour 

 lines are peculiarly shaped in the southeast quarter of the island. (Fig- 

 ure 12.) From a low depression a few kilometers west of Kilauea to 

 Cape Kumukahi, a distance of fifty kilometers, the lines are rather 



