500 LIEW JOU INMEUIL (UE CIE OILOG SZ, 
The rocks so far described show but little variation, and they are 
mainly important in their transition to the next series of eovolcanics 
which cover nearly one-half of the area. The acid eruptives include 
the eorhyolites and eodacites which chemically are almost identicaf 
with the younger rhyolites and dacites. They possess a porphyritic 
structure and a black felsitic groundmass. All the rocks described in 
the paper show strong mechanical deformations, but chemical altera- 
tion of the minerals in this series is so rare that it is probable they 
were broken during their eruption. The structure is almost crypto- 
crystalline, and it varies even in the same thin section. A considerable 
number of accessory minerals occur and pseudomorphs are quite com- 
mon. Epidote is present, as in the South Mountain rocks. In the 
eorhyolites eutaxitic structure is less common than in the other types. 
The groundmass is weakly doubly refracting and red in color due to 
hematite flakes. Among the pyroclastic rocks occur the volcanic 
equivalents of the porphyries. Quartz is rarely present, yet the rocks 
are more acid than the eodacites. Under the primary breccias are 
included the eutaxites and the agglomerate lavas, the former showing 
flow structure, the latter being fragmental. The agglomerates possess 
the rhyolitic structure of Rutley or the aschen structure of Migge, 
which argues for a tuff-like origin. The absence of foliation and 
transition into the eutaxites speaks against this view, thus leaving the 
question open. Near Kolsj6n occur fine examples of perlitic partings, 
spherulites and lithophyse. The chemical work of Santesson shows 
no essential difference from the younger eruptives. ‘The presence of 
manganese allies these rocks to the South Mountain types, and the 
high alkali percentage joins them with the keratophyres and dacites. 
In age the rocks are pre-Cambrian. Sederholm divides the 
Archean into three. divisions: Katarchean, Bottnian, Karelian 
(Algonkian). The Smaland granites and halleflinta are katarchzan 
and belong to the group of oldest known volcanics. ‘There are no 
safe mineralogical distinctions between the eovolcanic and the younger 
porphyries, but there is a difference of habit. In the older rocks there 
is a greater occurrence of crypto-crystalline structure and less of. the - 
granophyric or microfelsitic arrangement. The boundaries of the 
mineral constituents are indistinct, and there is a greater number of 
secondary constituents. Spherulites and other characters also enter. 
The eruptive character of the rocks is proved by : 
1. Absence of true stratification. 
