REPORT OF THE CHIEF ASTRONOMER 767 



SESSIONAL PAPER No. 25a 



aeter, it must be taken as confirming to a certain degree the hypothesis that 

 practically there is no bottom. 



' According to these views, the few small inclusions close to the margin 

 are those last detached and prevented from sinking by the increasing vis- 

 cosity of the cooling liquid. A block once well away from its original posi- 

 tion would not be held stationary, since the greater heat and liquidity at 

 short distances from the borders would permit a freer fall.'* 

 Bai'rell was finally allowed to publish his masterly monograph on the 

 Marysville stock, in which paper he shows, with unrivaled completeness, the 

 pertinent actual field relations which can be seen in a small body of this kind.f 

 He discusses the alternative hypotheses of batholithic intrusion and arrives at 

 results which are practically identical with the views of the present writer. He 

 did not consider the necessary consequence of stoping, namely, abyssal 

 assimilation. 



The present writer's statement of the hypothesis was published in the 

 American Journal of Science for 1903 and in Bulletin 209 of the United States 

 Geological Survey the same year. A supplementary paper was published in the 

 American Journal of Science in 1908. Since 1903, Andrews in Australia, 

 Barlow and Coleman in Ontario, Ball in Colorado (Georgetown Quadrangle), 

 Calkins in Idaho, (Coeur d'Alene District), and others working in Canada and 

 the United States have found the stoping hypothesis helpful in explaining 

 tield-relations. 



But the stoping-syntectic hypothesis cannot account for the rise of magma 

 through the whole of the twenty miles of earth-crust, which is the minimum 

 vertical distance between the substratum and the visible batholithic roofs. 

 Granting that the outer shell of the earth, one or two hundred miles in 

 thickness, is in approximate thermal equilibrium, the heat supply of the sub- 

 stratum is incompetent for such a prodigious work. The great basaltic floods 

 which have flowed out from fissures evidently did not reach the surface by 

 assimilating the acid shell overhead. That, notwithstanding their patent super- 

 heat, they assimilated but minimal amounts of this shell shows that they issued 

 rapidly, through narrow fissures in the acid shell. This old principle of abyssal 

 injection has long been recognised, but has seldom been phrased in terms of a 

 primary basaltic substratum. If, now, we imagine abyssal injections of the 

 same nature as those underlying basaltic lava fields but much larger (wider), 

 the phenomena of stoping and assimilation necessarily ensue. Some molar- 

 contact assimilation must also take place, but for the reasons above detailed, 

 should not rival abyssal assimilation in the preparation of secondary magma. 

 The combined processes of abyssal injection and assimilation must produce 

 bottomless magma chambers. This deduction is abundantly supported by all the 

 known facts about granitic rocks, and the separation of subjacent bodies in the 

 classification of intrusive formations seems to be genetic and, therefore, 

 demanded. 



* J. Barrell, Professional Paper No. 57, U.S. Geological Survey, 1907, p. 170. 

 t J. Barrell, Prof. Paper, No. 57, U.S. Geol. Survey, 1907. 



