442 Prof. Dr. T. G. Bonney — TroldoUte, etc., in Aberdeenshire. 



I possess a slide of the Volpersdorf troktolite, and have to thank 

 Prof. Judd for the loan of others, as well as of a slide of the same 

 rock from Baste. All these agree very closely with the rock described 

 above. In them also, diallage is sparing]}' present in narrow 

 irregular-shaped grains, so as not readily to catch the eye in hand- 

 specimens (one, however, of my specimens of Volpersdorf rock 

 has two or three conspicuous crystals of diallage). Hence we need 

 not hesitate to call the Belhelvie rock a troktolite or forellen stein. 



In my paper on the Serpentine of the Lizard (Quart. Journ. Geol. 

 Soc. vol. xxxiii. p. 906), I describe a rock from Covei-ack Cove, as 

 being almost identical with the forellenstein of Volpersdorf, and 

 this was afterwards confirmed by an analysis by Mr. F. T. Houghton 

 (Geol. Mag. Dec. II. Vol VI. p. 504).' The Coverack troktolite, 

 however, has probably a little more diallage than the Volpersdorf 

 rock, and in the specimen analyzed there was only 33 per cent, of 

 olivine as against 45 per cent, in the latter rock. Macroscopically 

 and microscopically, this Belhelvie troktolite looks even nearer the 

 Volpersdorf type than that of Coverack Cove. A chemical analysis, 

 however, for which I am indebted to the kindness of A. E. Brown, 

 Esq., B.Sc, of University College, London, shows that on the whole 

 the Belhelvie rock is more closely allied to the troktolite of Coverack 

 than to that of Volpersdorf, and the per-centage of AljOg is rather 

 larger, and that of MgO rather smaller, than my estimate founded on 

 microscopic examination led me to expect. The following is the 

 analysis (S.G. = 2-73). 



H,0 8-12 



Sib2 



i.ii 



S9-87 



A1303 



24-30 



Fe^Os 



1-59 



FeO 



4-09 



CaO 



7-61 



MgO 



11-30 



*K,0 



Ml 



mliO 



1-93 



99-92 



1 I append the analyses made or quoted by Mr. Houghton. I. is the Volpersdorf 

 rock, II. that of Coverack, III. the felspar of No. 1., IV. the felspar of No. II. 

 From the latter two it is evident the Coverack rock contains rather more labradorite 

 than the Volpersdorf rock. I think, however, that the specimen analysed of the 

 latter rock must have been a little richer than common in olivine. 





I. 



II. 



III. 



IV. 



HoO ... 



... 8-30 ... 



... 4-38 ... 



... 1-87 ... 



... 3-19 



Sibo ... 



... 41-13 ... 



... 45-73 ... 



... 47-05 ... 



... 49-65 



A1063 ... 



... 13-56 ... 



... 22-10 ... 



... 30-44 ... 



... 29-34 



FcOg ... 



Feb ... 



2-19 ... 

 ... 6-19 ... 



... o-7n 



... 3-51/ — 



1-56 ... 



... 0-59 



CaO ... 



... 6-72 ... 



... 9-26 ... 



... 16-53 ... 



... 12-18 



MgO ... 



... 22-52 ... 



... 11-46 ... 



... 0-09 ... 



0-46 



KoO ... 



u-83 ... 



... 0-34 ... 



... 0-78 ... 



... 0-48 



Na^O ... 



... 0-96 ... 



... 2-54 ... 



2-10 ... 



... 3-61 



102-40 100-03 100-42 99-51 



* Mr. Brown adds, " The values of these are uncertain — the numbers given are the 

 means of two experiments : the limits between which the value may lie are NajO 1-85 

 to 2-33, K2O 1-19 to -71.— Total 3-04." 



