320 The American Geologist. November, i«si5 
until indisi)utablo evidence is produced to the contrary — there exists 
now a certain element of doubt concerning- the accuracy of this view." 
u. s. G. 
Uebe)- postarcJuciscJieu Granit von Snlitehna in Nortvegen iind fiber 
das Vorkommen von s. g. Corrosionquarz in Gneisen unci Graniten. 
By Om^o Nordenskjold. (Bull, of the Geol. Dept. of the Univ. of Up- 
sala, vol. II, pt. 1. no. 3, pp. 118-128, 1895.) The district of Sulitelma, 
in 68° N. Lat., and on the border between Sweden and Norway, has 
been the subject of careful research by a number of geologists on ac- 
count of the occurrence there of rich copper ores. Occupied with sim- 
ilar research, the author had opportunity to study a granitic rock, in- 
teresting on account of its occurrence in the form of a laccolitic lens 
included between the mica slates, having a length of more than five 
kilometers and a breadth of at least 1,200 meters. The age of the 
schists is not known with certainty, but must be considered as post- 
Archean and i)re-Devonian. Though the granite (as well "im Hangenden 
als im Liegenden") very rarely and in small degree traverses the schists, 
it must be considered as younger and not cotemporary with them. Now 
it is interesting that, while all Swedish granites of post-Archean age 
when occurring in undisturbed positions are very well characterized, 
this rock — a porphyritic mica-granite, more or less gneissoid — much re- 
sembles the old Archean granites. The same appears to be the case 
also in other parts of the mountain districts in Scandinavia where gran- 
ites occur in the same position. The author concludes that they have 
all been intruded simultaneously with the folding of the rocks and the 
forming of the mountains, and have therefore obtained their layer-like 
position and their aspect of greater age. 
An interesting featvn-e in all these rocks is the great development of 
the structure, described by Fouque and Michel Levy under the name 
"quartz de corrosion," consisting of complex aggregates of quartz and 
feldspar, similar to the granophyric structure but distinctly different as 
the included quartz individuals are always limited by bent and curved 
lines. The author has studied this structure in a number of rocks and 
has found it very common in gneisses, but rather rare in eruptive rocks 
where it occurs only in rocks altered b}' dynamic action, it therefore is 
probable that it has always been formed in connection with dynamic 
metamorphism. The author has since seen in Paris, in the collection 
of Prof. A. Lacroix, a granitic rock of post-Carboniferous age from the 
Pyrenees, which, having taken part in the forming of mountains, is 
wonderfully like the rock from Sulitelma and shows the same structure. 
It is of great importance to distinguish the structure here mentioned, 
occurring in gneisses and altered granites, from the granophyric struc- 
ture found probably only in igneous rocks. 
