32 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol. 66. 



gabbro intrusive into quartzite have an uppermost layer of biotite 

 granite. Tliese are regarded as having originated from the fusion 

 and assimilation of the intruded quartzite. 



The view adopted includes what has been called the assimilation-differentiation 

 theory. The acid zone is thereby conceived as due to the digestion and assimila- 

 tion of the acid sediments, together with the segregation of most of the assimi- 

 lated material along the upper contact. 



This theory of differentiation has since been greatly amplified by 

 the same author.^^ It is interesting to quote the objection of Lewis ^* 

 to its application to the Palisade sill. 



A hypothesis of stoping or splitting off and engulfing slabs of overlying 

 strata, afterwards assimilated by solution in the magma, has been invoked instead 

 of some process of differentiation in explanation of certain facies eruptive rocks. 

 In case of the Palisade diabase, however, as in some cases at least to which this 

 theory has been applied, the process would seem to be mechanically impossible 

 on any important scale. The diabase is 20 per cent heavier than the inclosing 

 strata, and unless this was more than offset by expansion in the fused mass, it 

 would be impossible for sandstone or shale to sink into it, even if completely 

 broken away from the parent stratum. If stoping is possible at all in such cases 

 it must be underhand stoping, which the advocates of the hypothesis have not 

 yet claimed. 



The Gowganda Lake sills described by Bowen^'^ present some very 

 close analogies with the Goose Creek area, as may be seen from the 

 following quotations : 



The sills * * * are not alwaj's entirely composed of the dark gray diabase. 

 In places we often see little pink spots, found to be areas of micropegmatic 

 (quartz and albite). This material may increase in amount until it forms quite 

 the whole of the rock, giving rise to "red rocks" or granophyres. Moreover, 

 pink aplitic veins are often numerous in the sills. To the development of these 

 " red rocks " and their relations to the diabase and inclosing sediments atten- 

 tion will now be given. The sills almost uniformly show the albitic rocks at or 

 near their upper contacts. Summing up the evidence of the upper contacts of 

 the sills, just described, we have at the Foot Lake sill, in one place, the special 

 development of granophyric material in the diabase quite close to its contact 

 with altered slate or adinole, the granophyric interstices having practically the 

 same composition as the adinole and evidently derived from the latter by some 

 process of transfusion. A little farther south where the action has been more 

 intense a wider zone of adinole developed. Part of the adinole close to the 

 diabase has been to some extent recrystallized, giving the beginning of grano- 

 phyric structure. The writer believes that in the case of the Lily Lake and 

 Lost Lake sills the evidence points to a still more complete recrystallization of 

 part of the adinole with the production of tj'pical granophyre. In other words, 

 some of the adinole was essentially in a state of aqueous fusion and crystallized 

 as granophyre. The melt thus formed was to a certain extent free to diffuse 

 into the diabase magma and gave rise to the abundant granophyre interstices 

 near the granophyre. 



" Igneous Rocks and their origin. New York, 1914. 



'* Petrography of the Newark Igneous Rocks of New Jersey, p. 132. 



isjourn. Geol., vol. 18, pp. 667-69, 1910. 



