8 OLAF HOLTEDAHL. M,-N. Kl, 



all. The explanation Is: first, that many of the minor districts have their 

 Cambro-Siluric rocks so strongly altered by the surrounding igneous rock, 

 that but few and poorly preserved fossils are found, so that the district 

 has but small paleontological interest; or on the other hand, adjacant 

 regions may exhibit so great differences in both the paleontological and 

 petrological development of their sedimentary series, that for paleonto- 

 logical and stratigraphical purposes they naturally must be regarded as 

 two distinct areas even though no distinct dividing line is discoverable. 



The various districts that will be mentioned here, are, — commencing 

 from the north: 



The Mjøsen District, a very large area, that towards the north 

 passes into the metamorphosed regions of Central Southern Norway, 

 Throughout this district the folding of the strata has been strongly marked, 

 and in shales particularly the fossils have suffered much under the pressure; 

 Hadeland, passing to the south into Ringerike, From Tyrifjord and 

 towards the SSW along the western border of the Kristiania region we 

 find a strip of sedimentary land, consisting however, to a great extent of 

 highly altered rocks. On both sides of Lake Ekern we have Cambro- 

 Ordovicic beds, — the district of Eker, — but they are often somewhat highly 

 metamorphosed. Passing from the Tyrifjord to the south-east and east, 

 we reach the districts of Asker and Bærum, and further the Bundefjord, 

 with a series of small islands, to the south of the city of Kristiania. There 

 is a district, small but rich in fossils, that we shall call the Islands oflF 

 Holmestrand. Finall}^, at the southern end of the Kristiania region there 

 is the Skien — Langesund District, 



In the following tables I have shown the chief features of the present 

 classification of the Ordovicic-Siluric series of some of the districts of the 

 Kristiania region, and in these tables will be found the stratigraphie termi- 

 nology employed in the present paper. As it may be of interest to know 

 the petrological character of the various horizons mentioned, this has been 

 added to the table when not directly indicated in the stratigraphical name, 

 n order to give an idea of what is intended by the various zones, as 

 compared with those of well known foreign regions, the Ordovicic table has 

 been supplied with a column showing the principal divisions of the Ordovicic 

 system of Western Russia, which in most cases with great certainty can 

 be correlated with those of the Kristiania region. In the Siluric table 

 there is a column showing the principal divisions of the Welsh Siluric. 



As regards the thickness of the Ordovicic-Siluric sedimentary beds 

 belonging to the various stages, we may obtain an idea by referring to 



