298 Professor H. M. Posnett — On Geological Hypothesis. 



discovered. The effects of ' mixture ' have also been appealed to, 

 and it is possible that in some cases the minerals wbicli consolidate 

 out of turn may be ' xenocrysts,' derived from some ingested foreign 

 rock. But as a general explanation this admittedly cannot be 

 maintained. 



No doubt difficulties will also be found to attend any attempt to 

 explain anomalies by the presence of water, but it appears to me 

 that the attempt is worth suggesting. The problem as it now 

 presents itself is to show why certain minerals retain the fluid state 

 at a temperature below, often far below, that of the fusion-point: 

 thus, in the case of some examples of eeleolite syenite the question is 

 why plagioclase felspar crystallized out at a lower temperature than 

 orthoclase, orthoclase at a lower temperature than sodalite, and sodalite 

 than ^leolite. Can this be due to the effects of included water? To 

 answer this question definitely might not be difficult by means of 

 experiment. The determination of the fusion-points having been 

 accomplished, the next step that awaits us is the determination 

 of the temperatures at which the minerals in question crystallize 

 from solution. An investigation in this direction could not fail to 

 give interesting results. 



In conclusion, it may be pointed out that the results definitely 

 obtained in the case of quartz indicate that the temperature of 

 consolidation of granite might naturally be expected to be below 

 that of dolerite. The quartz of granite has consolidated at 

 a temperature below that of orthoclase and a fortiori below that 

 of plagioclase and pyroxene. The temperatures of fusion of these 

 two rocks, as observed in the laboratory, stand in inverse order to 

 the temperatures at which they consolidate in nature, owing to the 

 fact that in the case of fusion by artificial means water inlays 

 no part. 



HI. — A Word on Geological Hypothesis. 



By Professor H. Macaulay Posnett, LL.D., etc. 



"SCIENTIFIC men," said Professor Thomas H. Huxley,'^ "get an 

 O awkward habit — no, I won't call it that, for it is a valuable 

 habit — of believing nothing unless there is evidence for it ; and they 

 have a way of looking upon belief which is not based upon evidence, 

 not only as illogical, but as immoral." 



Quite so. There is no higher conception of truth — the most 

 exact knowledge attainable at the given time and place — no nobler 

 practice of truthfulness — the unflinching utterance of the most exact 

 knowledge we possess— than our best men of science constantly 

 display. And it is just because they are the world's highest 

 guardians of truth, the world's noblest exponents of truthfulness, 

 that our men of science are bound by the laws of their order to 

 set the study of facts before the acceptance or retention of any 

 theory, to expose in the clearest light any weak points in reasoning 

 that on the whole receives their approval, to boldly dwell upon the 



^ " Science and Hebrew Tradition," p. 65. 



