377 



in grains which show characteristic cleavages and optical properties. The 

 augite is a colourless mineral probably malacolite. The general characters 

 of the other minerals will be described later on. The constituents of the 

 rock are generally without definite form. The smaller constituents are 

 often present as extremely minute and more or less rounded (globulitic) 

 grains. 



The Ceratopyge-limestone is changed to a grey or bluish grey crystal- 

 line limestone, in which wollastonite, actinolite and vesuvianite have 

 sometimes been developed. 



The Phyllograptus-shales are converted into hornfels, chiastolite slate 

 or spotted clay slate. Chiastolite crystals and graptolites may occur in 

 the same rock. 



The division 3 c. of BROGGER comprises the Megalaspis-limestone, the 

 Expansus-beds (calcareous shales with impure limestone bands and nodules, 

 containing Asaplius expanx-us) and the Orthoceras-limestone. Owing to 

 its variability in lithological character and the abundance of fossils in 

 particular beds it presents most interesting metamorphic phenomena. 

 The Megalaspis-limestone was seen in one locality to have been converted 

 into a grey fine-grained marble. The Expansus-beds are usually con- 

 verted into thin alternating bands of flesh red (to violet) and blue (to black) 

 hornfels. The red or violet hornfels represents the nodules and layers of 

 impure limestone and the blue or black hornfels the intervening argillaceous 

 layers. A flesh-red hornfels from Bagstevold was found by microscopic 

 examination to consist of plagioclase, garnet, actinolite, colourless augite, 

 titanite and opaque grains (iron-ores or graphite). Sometimes the calcareous 

 nodules and bands have been converted into crystalline limestone instead 

 of being replaced by silicates. The forms of fossils are often preserved 

 in rocks containing wollastonite, malacolite, sphene, garnet, actinolite. 

 Thus, in a violet hornfels from Gunildrud shells of brachiopods are 

 replaced by coarse granular aggregates of calcite, wollastonite and 

 magnetic pyrites ; the casts of the shells being composed of compact 

 violet hornfels. 



Casts of Orthis caligramma in garnet occur in a garnet-hornfels from 

 the same locality. The garnet which forms a fourth or a fifth of the entire 

 mass of the rock is partly idiomorphic and partly in the form of the 

 brachiopod. The Orthoceras-limestone is converted into crystalline 

 marble in which various silicates (wollastonite, vesuvianite, garnet and 

 actinolite) have been developed. In one case a thin stratum of the 

 rock was entirely composed of a granular aggregate of wollastonite and 

 garnet. Macroscopic and idiomorphic vesuvianite and garnet may be seen 

 in some specimens. 



It appears, therefore, from the researches of BROGGER, that the more 

 argillaceous deposits are converted into spotted clay slates, compact 

 hornfels and chiastolite slates, and that the calcareous rocks may either 

 furnish a crystalline marble or a rock entirely composed of silicates. In 

 the majority of cases the alteration is accompanied without any important 

 change in the chemical composition of the rock, but in the case of the 



