Vol. 50.] BASIC ERUPTIVE ROCKS OF GRAy. 25 



in the neighbourhood of the above-mentioned basic boss-rocks, 

 whereas other kinds of dykes appear very seldom. I have observed 

 only a small number of rhomben-porphyries (plagioclase-rhornbeu- 

 porphyry and common rhomben-porphyry, 7 or 8 great dykes partly 

 followed along a stretch of more than 20 kilometres = 12^ miles), 

 mica-syenite-porphyry and ajgyrine-syenite-porphyry (Solvsberget), 

 8 to 10 greater dykes ; finally, a number of diabase-dykes, etc. On 

 the other hand, the dykes and sheets of bostonite and camptonite 

 outside this tract, in which the basic boss-rocks occur, are very 

 sparsely distributed in the Christiania region, and not in the same 

 typical varieties as in Gran parish. 



On Brandberget a hornblende-bearing rock, closely allied to camp- 

 tonite, locally appears as an unquestionable contact-facies of the 

 olivine-gabbro-diabase. 



In the small laccolitic sheet south of Eilden camptonite is tho 

 main rock ; pyroxenite appears here only subordinate and mostly in 

 the central parts ; and all the passage-types between camptonite 

 and pyroxenite are found. At Solvsberget also I have collected a 

 rock of the camptonite-bostonite series, an intermediate type be- 

 tween both extremes, occurring localty as a contact-facies. 



The above observations conclusively prove that the camptonites 

 and the bostonites are nearly connected with, and must be derived 

 from, the same magma as the previously-described boss-rocks. 



The mutual rolation of age between the camptonites and the 

 bostonites is invariably as follows : — 



When dykes of bostonite and camptonite cut each other, the 

 former, without exception, is the younger. 



In a bostonite (from Lindberget, on Lake Maena) I have found 

 rounded enclosures of basic masses partly of camptonite, partly of 

 pyroxenite ; these enclosures can only be explained as early crystal- 

 lizations of basic composition in a magma, from which the distinct 

 magma of the bostonite was not yet separated as a final product of 

 tho differentiation. 



In seven different localities (chiefly in Xaes, south-west of 

 Brandberget) there appear considerable sheets of bostonite-breccia ; 

 the main localities of these breccias in Noes are situated on the 

 continuation of the great fault-fissures of Lake Randsfjord, and 

 farther north-north-east continued in tho fault-crevice along the 

 bed of the Huns river. Tho breccias are brimful of angular 

 fragments of Archaean schists and Silurian slates (chiefly alum- 

 shales) and limestones of the lowest etages (1-3), all the fragments 

 being cemented by a bostonite groundmass. In several blocks of 

 this breccia I have observed that every fragment is surrounded by 

 a more basic dark-green mass, partly of camptonitic composition ; 

 this basic matter, enveloping the angular fragments, is then itself 

 embedded in the scarce bostonitic groundmass. In a similar breccia 

 from Augedal I found a rounded lenticular mass of camptonitic rock 

 ^ metre (13 inches) in diameter; this mass showed, on chemical 

 analysis, an undoubted camptonitic composition. 



