36 SCIENCE PROGRESS 



phosphorus-metasomatism, and siHca-metasomatism. He shows 

 that the laws of mass action apply in general to meta- 

 somatism, one important result being that in order to effect 

 replacement, the solutions must reach a definite minimum con- 

 centration for each case. This explains why metasomatic 

 processes are common, but not as universal as the solutions 

 themselves, since the solutions can only occasionally reach the 

 necessary minimum concentration. 



Phenomena of the same order as those described by Gold- 

 schmidt have been dealt with in a more general manner by the 

 late Prof. J. Barrell in his paper (edited by F. F. Grout) on 

 " The Relations of Subjacent Igneous Invasion to Regional Meta- 

 morphism " (Amer. Journ. Set. (V), 1921, 1, 1-19 ; 174-86; 

 255-67), Barrell seeks to show that regional metamorphism 

 is due more to igneous invasion than to depth and pressure. 

 Some regions where the rocks have indubitably been deeply 

 buried and closely folded show very slight metamorphism ; 

 others, in positions where depth can have had only small in- 

 fluence, show the highest grades of recrystallisation. He 

 considers that recrystallisation in schists and gneisses is largely 

 due to the emanations proceeding from subjacent batholiths. 

 The suggestion is made that there is a rhythm between igneous 

 activity and crust movement, injection of magma, and earth 

 movements leading to foliation especially in the softened and 

 weakened rocks adjacent to the batholith, alternating with one 

 another. The activity of solutions and selective crystallisation, 

 in a word, metasomatism, in the recrystallisation of rocks, is 

 emphasised throughout, just as it is in Goldschmidt's work. 

 Following a similar line of thought to Barrell 's, Sederholm has 

 wTitten an interesting discussion of the contrast in structures 

 and mineral composition between rocks which have suffered 

 folding of the Alpine type, and those which make up the 

 Grundgebirge of Scandinavia, Canada, and other Archaean 

 regions (** Faltung und Metamorphose in Grundgebirge und in 

 Alpinen.Gebieten," Geol. Foren. Stockholm Fork., bd. 41, hft. 3, 

 19 1 9, 249-56). The Alpine type is due to the action of directed 

 pressure near the surface of the crust ; while the Grundgebirge 

 type represents the rocks which have been pressed down into 

 depths where uniform pressure is the rule, and where they have 

 come under the thermal influence of regional plutonic magmas. 



Mr. C. E. Tilley has recently published a notable set of 

 papers on the ancient metamorphic rocks of the Eyre Peninsula, 

 South Australia. The granite-gneisses of this region {Q.J.G.S., 

 1 92 1, 77, pt. 2, 75-134) besides the normal biotite and horn- 

 blende-bearing varieties, include pyroxene-granites of the 

 charnockite series and a great development of garnet-gneisses. 

 The gneissic banding is held to be a primary flow structure in 



