REPORT OF THE CHIEF ASTRONOMER 733 



SESSIONAL PAPER No. 25a 



fluid lava. There is no reason to believe that exothermic reactions are of any 

 moment under the conditions. Since, as we have seen, vertical currents are 

 soon inhibited, the continuance of solution at the roof waits on conduction. 

 Unless we postulate a degree of superheat utterly without parallel in the hottest 

 volcanoes, such as at Kilauea, at Mauna Loa, and at Matavanu, Savaii, the 

 extensive solution implied by this hypothesis is impossible. 



The favorite conception of the French geologists, that the necessary solution 

 of the roof rocks has been due to the influence of juvenile gases (agents 

 mineralisateurs), rather than to direct solution in liquid magma, is likewise 

 difficult to accept. Because the specific heat of a gas at low pressures is extremely 

 small as compared with that of rock-matter, we perceive that a quite incredible 

 amount of gas is necessary to liquefy thousands of feet of roof rock by blow- 

 piping, or by its mutual solution with the gas. There is no general physical 

 cause for a return of gas to the depths after it has done its solvent work. It 

 must collect at the batholithic roof either free or dissolved in the syntectic 

 magma. In either case its tension must increase and when the accumulation 

 approaches the limit implied in the hypothesis, the gas pressure must rise far 

 beyond that which the earth's crust could endure. The fact is that volcanic 

 action is not always, nor even generally, the result of batholithic intrusion. 

 We know that the implied crustal catastrophes, indefinitely greater than Kraka- 

 toan explosions, have not occurred in post-Cambrian time at least. Juvenile 

 gfases may bore the holes at volcanic vents and they have doubtless aided some- 

 what in the underground solution of rock; but it seems impossible to believe 

 that they are the leading agents in fashioning batholithic chambers, even for the 

 moderate depths exposed by erosion. 



The old idea that batholiths are simply geosynclinal sediments which 

 have been fused by the rise of the isogeotherms, has been recently revived by 

 Haug.* Space is lacking for the full discussion of this speculation, nor at this 

 day is it necessary to lay the ghost again. A few remarks will suffice to show its 

 inapplicability to the batholiths on the Forty-ninth Parallel. 



The Rocky Mountain geosynclinal is one of the thickest on record. Crustal 

 movements have exposed its lower beds at many points; yet they are not fused. 

 The same is true of the basal beds of the Cretaceous geosynclinal of the 

 Hozomeen range and California, each nearly 30,000 feet thick. On the other 

 hand, many batholiths have appeared in deformed geosynclinals of much less 

 thickness. Examples are seen in the Coryell batholith and that which has so 

 many satellites in the Boundary Creek district of the Columbia range. 



Again, the speculation may be dismissed because of its manifest failure to 

 provide the necessary heat supply. The lowering of the ' fusion-point ' of 

 average sediments by admixture of the ' agents mineralisateurs ' can hardly be 

 supposed to give a magmatic temperature below 500° C for a batholith. Yet no 

 known geosynclinal is thick enough to have assumed this temperature in its 

 lower beds through the rise of the isogeotherms. Haug does not, therefore, 

 essentially improve the speculation by an appeal to the rather mystical ' agents 



* E. Hang, Traite de Geologie, tome 1, Paris, 1907, p. 188. 



