224 W. H. Hobbs — Par agenesis of Allanite and 



von Fritsch* described this mineral in the granitite of Ilmenau 

 in the Thuringian Forest. Yom Rathf recognized it as an im- 

 portant accessory constituent of the tonalite of Mt. Adamello. 

 Interesting occurrences are mentioned by Liebisch^: in the 

 granite porphyry of Erdmannsdorf and other localities in 

 Lower Silesia, and by Tornebohm§ in an amphibole-biotite 

 granite from Eastern Siberia. Our knowledge of the optical 

 properties of allanite has been much advanced by the investi- 

 gation of this mineral in the granite of Pont Paul near Mor- 

 laix, Finisterre.| 



The occurrence of allanite and epidote as constituents of the 

 same rock has been several times observed, and by two inves- 

 tigators these minerals have been found so intergrown, as to 

 add evidence of isomorphous character to that already known 

 to exist in the similar crystal form and analogous chemical 

 composition. 



In 1854, Blomstrand^f described from Wexio in Sweden 

 crystals of pistazite arranged radially about cores of allanite ; 

 and somewhat later Ewald Becker** mentioned inclusions of 

 orthite in the epidote of a granite from Striegau. Messrs. 

 Cross and Iddingsff observed apparent inclusions of epidote in 

 allanite. It is further stated in many text-books^ that cores of 

 allanite in epidote and cores of epidote in allanite, occur at 

 Sillbohle in Finland. After some search I am unable to des- 

 ignate the original paper by Nordenskiold, but through the 

 courtesy of Professor Wiik of Helsingfors, I have a copy of 

 the catalogue to the mineral collection of the Helsingfors Uni- 

 versity§§ in which the interesting intergrowths are figured. A 

 similar intergrowth has been recently found by T6rnebohm|| 

 to characterize the epidote-gneiss of a considerable portion of 

 Wermland. " Small crystals which have been taken for orthite 

 and which are crystallographically similar and oriented like 

 their host, occur in the epidote."^[^[ 



* Geognostische Skizze der Urngegend von Ilmenau im Thuringer Walde. 

 Zeitsch. d. d. Geol. Ges., xii, 105. 



f Beitrage zur Kenntniss der eruptiven Gesteine der Alpen, I, ibidem, xvi, 255, 

 1864. 



% Ueber die Granitporphyre Niederschlesiens, ibid., xxix, 725, 1877. 



§ Vega Expedition IV, 115-140, Stockholm, 1884. Ref. Neues Jahrb. f. Min., 

 etc., 1885, i, 429. 



I Michel Levy et Lacroix. Note sur un giseraent francais d'allanite, Bull. soc. 

 miner, de France, xi, No. 2, 64, Feb., 1888 



I Blomstrand, Oefvers. af akad. Forhandl., 1854, No. 9, p. 296. Ref. Journ. f. 

 prakt. Chem.. lxvi, 156. 



** Ewald Becker, Ueber das Mineralvorkommen im Granit von Striegau ins- 

 besondere uber den Orthoklas und dunkelgriinen Epidot, Breslau. 

 ff Loc. cit. 



%% Dana, Brooke and Miller, etc. 

 §§ F. J. Wiik, 1887, p. 27, pi. II, fig. 7. 



II Tornebohm. Mikroskopiska bergartsstudier, XIII Epidotgneiss. Geol. For. i 

 Stockholm Forhaudl., 1882, No. 75, vi, 189. 



H Ref. Cohen, Neues Jahrb. f. Min., etc., 1883, i, 245. 



