R. A. Daly — Mechanics of Igneous Intrusion. 289 



the greater depths, exceedingly important, " ansserordentlich 

 bedeutend."* Several cases have been described in which 

 even marginal assimilation at great depths has affected batho- 

 lithic magmas, though, as we have already seen, such cases are 

 exceptional. 



Since it is probable that magmas are more or less completely 

 saturated solutions, f there would doubtless be a volumetric 

 increase on the fusion of each block at whatever depth it attained, 

 an increase comparable to that demonstrated in fusion experi- 

 ments at 1 atm. of pressure. The question at once arises as to 

 what compensation can be made for the increased bulk of rock- 

 matter below the earth's surface incident to abyssal assimilation 

 on a large scale. Two possibilities suggest themselves in the 

 face of the hydrostatic problem involved. Either volcanic 

 outflow elsewhere, or secular upheaval in the region, would 

 satisfy the conditions. The latter would seem to be more 

 likely of fulfillment in regard to stocks and batholithic intru- 

 sions generally. It is to be noted that magmatic stoping 

 would tend to weaken the earth's crust immediately above the 

 intruding body, and there secular elevation of the surface 

 would be particularly looked for. There may, in this way, be 

 found one cause of the huge buckles filled with the " central 

 granites" of alpine mountain chains. This implies that the 

 doming of the great intrusive masses of the Christiania 

 Region, attributed by Brogger to laccolithic injection, may, in 

 reality, be due to this crustal weakening and buckling by mag- 

 mas working up from the " ewige Teufe." But, at present, it 

 must remain only the suggestion of a possibility, as the writer 

 has no personal knowledge of the region. 



It is, moreover, worthy of inquiry whether this sort of live 

 energy of intruding granitic magma may be responsible for 

 many of the well-known cases where the secondary structure- 

 planes in the invaded formations wrap around their respective 

 intrusive bodies. Examples are seen in the highly developed 

 peripheral cleavage and schistosity parallel to the outlines of 

 such magmas in the Rainy Lake region,;}; in the Black Hills,§ 

 and in the Sierra Nevada. || Such structures would certainly 

 be produced by the force of magmatic expansion, provided that 

 force be sufficient in amount, for it must be exerted always 

 normal to the chamber-walls. 



-Op. cit., iii, 350(1898). 



fLagorio, Tscher. Min. u. Petrog. Mitth., viii, 504 (1887). Cf. Delesse, 

 Bull. Soc. Geol. France (2), iv, 1398 (1847). 



% Lawson, Ann. Eep. Geol. and Nat. Hist. Survey, Canada, 1887, Pt. F, map. 



§ Van Hise, 16th Ann. Eep. U. S. Geol. Survey, Part I, 1894-5, pp. 637 

 and 815. 



|| Turner, 17th Ann. Report U. S. Geol. Survey, Pt. I, 1895-6, p. 555. 



