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PROCEEDINGS OF THE AMERICAN ACADEMY. 



flows. (Figure 15.) This body, shown in complete section, is only about 

 150 meters long by 18 meters in thickness in the middle, thickest part. 

 Its roof, still essentially unaffected by erosion, is little more than 

 140 meters thick. The rock of this small body is holocrystalline, wehr- 

 litic in chemical composition, but having enough plagioclase to place it 

 among the ultrabasic olivine gabbros. The body shows chilled contact 

 phases and its injected origin cannot be questioned. We have here. 



To/> o/ lA/esf IVa// of /f/'/<yc/ecf 





> 



Figure 15. Diagrammatic view of wall of Kilauea at the Uwekahuna sta- 

 tion, showing ultra-basic porphyritic gabbro injected into older volcanic lay- 

 ers. The "laccolith," arching the ash-beds above it, is about 150 meters in 

 length. About natural scale. 



barring volcanic perforation of the roof, a true homologue of the laccolith 

 postulated to explain the peculiar history and relations of Kilauea. 



In summary, we note the convergence of several independent lines of 

 argument in favor of the suggested hypothesis. It seems justifiable to 

 class Kilauea tentatively as the living vent of a still liquid satellitic 

 injection. We may also conclude that it is unsafe to deny, simply 

 because of the hydrostatic independence of the two active Hawaiian 

 lava columns, that a primary fluid substratum of basaltic composition 

 underlies the whole island. 



A n Icelandic Example. — Reck has suggested that the crater of the 

 Hrossaborg in central Iceland is a gas-exploded opening (diatreme) in 



