38 SCIENCE PROGRESS 



yield numerous types of ortho- and para-gneisses, along with 

 granulites and graphitic mica schists. 



H. Backlund has investigated a large collection of gneisses 

 and schists from the Taimyr region of Northern Siberia brought 

 back by the Russian expedition of 1900-2 under Baron E, von 

 Toll (" Petrogenetische Studien an Taimyrgesteinen," Geol. 

 Foren. Stockholm Fork., 191 8, 40, 101-203). A large granite 

 batholith is there in contact with a very varied series of gneisses 

 and schists, the degree of crystallisation of which is highest 

 against the igneous rock. Backlund further describes the 

 curious mineralogical consequences of orogenic movement 

 in these rocks, whereby a complicated and closely set system 

 of shearing planes has been produced. Numerous types of 

 hornfels and mylonite are also described. The paper con- 

 stitutes a notable addition to the literature of metamorphic 

 rocks. 



While most of his report (" Report on the Geology and 

 Geography of the Northern Part of the East African Pro- 

 tectorate," Colonial Repts., Miscellaneous, No. 91, E. A. 

 Protectorate, 1920, pp. 29) deals with the later igneous rocks, 

 Mr. J. Parkinson has also an interesting note on the gneisses and 

 schists of the region described. Granitic orthogneisses, horn- 

 blende gneisses and schists of polymorphic origin, and a series 

 of quartz-schists, marbles, etc. (Turoka Series), of clearly sedi- 

 mentary origin, are described. The igneous gneisses contain 

 marbles and abnormal gneisses with epidote, garnet, horn- 

 blende, sphene, scapolite, and carbonates, which are held to 

 be due to the partial or complete absorption of a pre-existing 

 sedimentary series, and are similar to described examples in 

 Mozambique and Canada. 



The metamorphism of the Mona Complex of Anglesey is 

 ascribed by Mr. E. Greenly in his recent monumental work 

 (" The Geology of Anglesey," vols, i and ii, pp. 980, Mem. Geol. 

 Surv. Gt. Britain, 191 9) to the effects of superimposed foldings. 

 There are three primary recumbent folds piled one on the other, 

 and in each the intensity of the metamorphism decreases 

 upwards. The metamorphism is believed to be a function of 

 the thickness of cover present when the fold was developing, 

 not of the subsequent cover ; so that metamorphism could 

 develop in a higher fold without appreciably increasing the 

 metamorphic grade of a subjacent fold. As the dynamic 

 metamorphism could only take place at the locus of folding, 

 the lower folds were metamorphically inert when the upper 

 and later ones were developed above them. There is a great 

 wealth of observation and theory concerning metamorphic 

 rocks in Mr. Greenly's work, which it is quite impossible to 

 summarise adequately here. 



