Revie w of Recent' Geolgical Literature. 313 
22. per cent, andesine is 1G.5 per cent, oligoclase and soda-bearing 
orthoclase are wanting and quartz is 11.7 per cent. This variation 
continues to diminish toward the body of the sill until the endo- 
morphic alteration fades out into the normal sill rock. 
The rock at 15 feet from the upper contact belongs to the gran- 
ite family. Toward the sill the rock varies more and more to- 
ward the gabbro type and toward the contact the variation is more 
and more toward granophyre granite. Xenoliths from the quartzyte 
present the same zones of metamorphism. 
The author calls attention to similar cases of profound altera- 
tion at contacts of basic intrusives on siliceous clastic rocks in 
Minnesota and in Ontario, viz: at Pigeon point and at Sudbury, 
where have been described granitic and intermediate rocks resulting 
from such contact, acting themselves as igneous rocks and forming 
characteristic intrusions in the manner of dikes. 
These phenomena are regarded by the author as demonstrating 
the assimilation theory at the points discussed. In his synthetic 
discussion he makes the following remarks: 
"The secondary origin of granite has long been maintained by 
N. H. Winchell who has referred to the Pigeon Point case as among 
others, demonstrating the fact.* Bayley came to the same belief 
for the granite and granophyre of the point but he did not extend his 
argument in detail to coyer other occurrences among the Minne- 
sota intrusives. On the other hand the principle, has not been ac- 
cepted as applying to these localities even by Van Hise whose rare 
knowledge of Lake Superior geology must give his opinion excep- 
tional weight.t Even the latest text books of geology give most 
inadequate treatment of the doctrine though it refers to one of the 
most important problems in the whole field of geology. Doubtless 
the majority of petrologists are to-day unfavorable to the assimila- 
tion theory of granite and its relatives except as it applies to a 
very limited, in point of volume insignificant, modification of cer- 
tain magmas at their contacts. 
"Van Hise's chief argument against the contact origin of the 
Pigeon Point granite emphasizes the fact that that rock has not 
the chemical composition either of the sedimentary formation or 
(as especially shown in the surplus of alkalies and the deficiency of 
iron in the granophyre granite) of a direct mixture of gabbro and 
sediments.! The much quoted argument of Brogger with refer- 
ence to the Norwegian granites is based on a similar fact.§ Many 
other writers have, on a similar ground, excluded contact assimila- 
tion as playing any considerable part in the formation of abyssal or 
hypabyssal magmas. 
"In practically every case the .opponents of the assimilation 
theory have treated of the assimilation as essentially a static phe- 
* Final Report, Minnesota Geological Survey, vol. ■">. p. 62, etc, L900. 
t Monogntph 47, IT. S. Geol. Sur., 1904, pp. 730-733. 
% Op. cit., p. 7:::;. 
§ Die Kruptivscstcine <l<-s Christianiagebietes. Pt. -. 1895, p. 130. 
