DALY. — THE NATURE OF VOLCAXIC ACTION. 115 



the coastal belt, it is probable that neither old strands nor coral de- 

 posits are here to be found at any notable heights above sea-level. 

 However, that fact, however fully demonstrated, could not invalidate 

 the laccolithic h}-pothesis. Highly Huid laccoliths like that at Shonkin 

 Sag do not disturb the strata into which they are thrust, to a greater dis- 

 tance from the edge of each laccolith than that equal to one-twentieth or 

 one-tenth of the laccolith's horizontal diameter. Even for more viscous 

 intrusions, like that at the classic Mt. Hillers in the Henry Mountains, 

 this distance is less than one-tifth of the diameter. There is no sure 

 reason for thinking that the edge of the Kilauea laccolith was near 

 enough to the seashore of the pre-intrusion period to displace the coast- 

 line materially. It is also important to observe that a fault runs 

 roughly parallel to the longer axis of the great arch for a distance of 

 about thirty-five kilometers. It is located from three to five kilometers 

 inside the shore-line. Its downthrow throughout is on the seaward 

 side, and the amount of throw varies from about 100 meters to 500 

 meters or more. (See Figures 12 and 14.) 



The maximum displacement is registered in a remarkable cliff south 

 of Kilauea. (Figure 14.) This greatest of all the pure fault-scarps 

 in the island finds its own explanation, if we correlate the displacement 

 with the upthrust incidental to the laccolithic injection. 



7. The generally accepted hypothesis that Kilauea is a primary vent 

 like ^lokuaweoweo, entirely fails to explain the fact that we have no 

 certain trace of a lava outflow over the wall of Kilauea. It places no 

 difficulty in the way of the h}'pothesis here outlined. 



8. Nevertheless, it is significant that, while Kilauea is less violent 

 in its eruption than Mokuaweoweo, the lower vent is the more ooncinu- 

 ously active. The latter contrast finds simple explanation on the 

 laccolithic hypothesi.s, which implies that the magma chamber of 

 Kilauea, below the cylindrical vent, is much nearer the earth's surface 

 than is the vaster magma chamber feeding the long pipe of Mokuaweo- 

 weo. The lodger pipe is evidently liable to the more ready discharge 

 by eruption through lateral fissures, and the space voided by such a 

 discharge must, on the average, be greater than that voided in a dis- 

 charge of Kilauea. A minute subsidence of the laccolith's nearly flat 

 roof after a major discharge at Kilauea would be much more rapid than 

 a similar settling of the thick roof over the main, probably narrower 

 and more fissure-like chamber beneath Mokuaweoweo. 



9. Finally, the laccolith ha.s been imagined with the help of an ac- 

 tual example. Under the Uwekahuna triangulation stiition in the wall 

 of the Kilauean sink, the writer found a small, but typical laccolith 

 which arches the basaltic flows above it, aud rests on older flat-lying 



