4o8 PETROLOGICAL ABSTRACTS AND REVIEWS 



of Caledonian age, which are partly green lavas, partly members of the opdalite- 

 trondhjemite group discussed in a previous paper. Locally on the borders of 

 the district are conglomerates, arkoses, and sandstones essentially of Downton- 

 ian age (Upper Silurian). Still younger dikes of diabase traverse the other 

 rocks, and Quaternary sands and clays, partly glacial, are the last deposits to 

 be laid down. 



The pre-Cambrian rocks are chiefly granitic, with lesser amounts of amphib- 

 olites. Structurally they represent a major syncline, the axis of which 

 parallels the trend of the Caledonides, i.e., runs northeast-southwest. The 

 phyllite division of the Cambro-Silurian is definitely assigned to the Cambro- 

 Ordovician on the basis of fossils occurring outside the area; it begins with a 

 basal conglomerate, and passes into phyllites and calcareous strata, with local 

 increase in sandy content. This phyllite division is at least 300 meters thick. 



The green saltes are assigned to the Silurian also on the basis of fossil find- 

 ings. These "slates" bear sandstones and conglomerates (rarely) and consid- 

 erable amounts of limestone and dolomite (which may have been derived 

 metasomatically from limestones), but metamorphosed clayey deposits are 

 predominant among the sediments. Eruptive rocks are highly metamorphosed, 

 so that they cannot always be assigned with certainty to volcanic origin. 



Sedimentary rocks are known from the Caledonian; they consist of con- 

 glomerates, typical sandstones, arkoses, and similar types, derived largely 

 from the pre-Caledonian and Caledonian effusives. Hence also these actually 

 follow the Caledonian opdalite-trondhjemites and green lavas. A description 

 of the first of these two Silurian types is to be found in the preceding review; 

 both basic and acid rocks are known, the latter including adamellite, granite, 

 and quartz-pegmatite. 



The Cambro-Silurian rocks were deposited on a peneplained surface. This 

 period of sedimentation was followed by one of intrusion — that of the opdalite- 

 trondhjemite group, either synchronously with or slightly preceding the 

 Caledonian mountain-building, during which sediments and intrusives alike 

 were folded and fractured, the magmas perhaps being deformed even before 

 complete congealing. Finally in late Caledonian times there was extensive 

 faulting of all the rocks of the Stavanger District. 



A study of the opdalite-trondhjemite masses of Stavanger demonstrates 

 that the larger intrusives are limited to the boundary between the phyllites 

 and the overlying green slates. These actually represent one type of structure, 

 whereas an entirely different type is indicated by flat-lying masses of intrusives 

 that seem to have been more severely displaced during cooling. In the Stavan- 

 ger District the two types of structures, one representing igneous rocks cooled 

 in place, the other those cooled after some dynamic action, lie close together; 

 of these the distorted and "dynamo-transported" masses are by far the more 

 common. 



After this general discussion of the geology of the region, the writer proceeds 

 to a description ot the metamorphism that has affected the rocks, with special 



