It. A. Daly — Mechanics of Igneous Intrusion. 19 



Like the first and second papers, this one does not present a 

 complete discussion of the different topics. On another 

 occasion the writer may publish a fuller statement of the 

 favored solution of the complex problem. 



Hypothesis of magmatic storing. — The essential points are 

 the following : 



1. Each acid, batholithic magma has reached its present 

 position in the earth's crust largely through the successive 

 engulfment of suites of blocks broken out of the roof and 

 walls of the batholith. 



2. The blocks (xenoliths) are completely immersed in the 

 magma, partly through the confluence of apophyses which 

 have been injected on joints and other planes of weakness in 

 the country-rock; more often the blocks represent the effect of 

 shattering, due to the obviously unequal heating of the solid 

 rock at magmatic contacts. 



3. The sunken blocks must be dissolved in the depths of 

 the original fluid, magmatic body, with the formation of a 

 " syntectic,"* secondary magma. 



\. The visible rock of each granite batholith or stock has 

 resulted from the differentiation of a syntectic magma. 



In applying the hypothesis to the explanation of actual 

 field-occurrences other general considerations seem necessary. 

 Stoping and abyssal assimilation on the batholithic scale are 

 begun by a primary basaltic magma. This magma carries the 

 heat required for the double action. f The source of the 

 magma is to be found in a general basaltic substratum beneath 

 the earth's solid crust. The crust is considered as composed 

 of two shells. The lower shell is capable of injection by 

 huge masses from the substratum, which retains open com- 

 munication with the injected bodies. The latter are regarded 

 as then stoping their way up into the overlying shell, in which 

 the resulting derivatives of the syntectic magma are the 

 visible batholithic granites and allied rocks. 



These subsidiary elements of the problem here to be dis- 

 cussed have been described in the first intrusion paper and, 

 more fully, in a later communication on " Abyssal Igneous 

 Injection."^ No one of these additional conceptions is essen- 



*This very convenient name for a magma rendered compound by assimi- 

 lation or by the mixture of melts, has been proposed by F. Loewinson — ■ 

 Lessing, Comptes Kendus, 7 e session, Congres geol. intermit. St. Petersburg, 

 1899, p. 375. 



f Whether the substratum is actually or only potentially fluid is not a 

 vital question in this connection. T. J. J. See, as a result of his calcula- 

 tions, holds that the earth's interior may be fluid. He explains the observed 

 rigidity of the planet as due not to its being a true solicf but to the direct 

 influence of gravity, which binds the earth-shells so effectively that bodily 

 tides are almost wholly prevented. In any case rigidity and solidity are not 

 svnonvmous terms. Cf. T. J. J. See, Astron. Nachrichten, v. clxxi, p. 

 378, 1906. 



{This Journal, vol. xxii, 1906, p. 195. 



