BIOCHEMISTRY 35 



that liver lecithin contains more than one unsaturated fatty 

 acid and that the individual acids differ in their degree of un- 

 saturation. 



The present paper describes the identification of these acids 

 as oleic acid, which predominates, and arachidonic acid. The 

 isolation of the latter acid is of interest in the light of Hartley's 

 work (/. Physiol., 1908-9, 38, 353), who found the unsaturated 

 acids of liver fat to yield a fatty acid which was oxidised to 

 tetrahydroxy-arachidic acid and gave on bromination a bromide 

 probably octobromarachidic acid. 



Levene and Simms think that the liver may contain several 

 lecithins and that oleyl lecithins predominate. 



GEOLOGY. By G. W. Tyrrell, F.G.S., A.R.C.Sc, University, 

 Glasgow. 



Metamorphism and Metamorphic Rocks. — Prof. V. M. Gold- 

 schmidt has described in detail the intensification of the regional 

 metamorphism of the clay-slates of the Caledonian fold-moun- 

 tain region of Southern Norway around certain masses of 

 granite (" Die Injektionsmetamorphose im Stavanger Gebiete," 

 Vidensk. Skrift. I. Math. Nat. KL, Kristiania, 1920, No. 10, 

 pp. 142). In the Stavanger district the regional rock type is 

 a quartz-muscovite-chlorite-phyllite. The first stage of " in- 

 jection-contact-metamorphism " is the formation of a garneti- 

 ferous zone, then come porphyroblastic albite-schists, and, 

 finally, augen-schists and injection-gneisses (lit-par-lit-gneisses). 

 Chemically the increasing metamorphism is characterised by 

 additions of silica and soda, possibly also lime, and the sub- 

 traction of water. The new-formed albite is believed to be 

 due to the combination of sodium-silicate solutions (" water- 

 glass ") derived from the igneous rock, with the excess alumina 

 of the phyllite. In the change from phyllite to albite-schist 

 there is a considerable volume increase, and it is possible that 

 this accounts for the ptygmatic folding (Sederholm) of the 

 injection-gneisses. The metasomatic processes in this and 

 other kinds of metamorphism are emphasised, and a detailed 

 classification of metasomatic alterations in schists is given. 



Goldschmidt has further elaborated his views on the meta- 

 somatic processes in silicate rocks in a recent paper (Econ. Geol., 

 1922, 17, 105-23). He distinguishes between metasomatism 

 with the addition of metal compounds, and with the addition 

 of metalloids or their compounds. Under the former are 

 included alkali-metasomatism, magnesia-metasomatism, iron- 

 metasomatism, and nickel-metasomatism, involving the addi- 

 tion of salts of these respective elements ; under the latter 

 there are included fluorine-chlorine-boron-metasomatism, sul- 

 phur-metasomatism, water and carbon-dioxide metasomatism, 



