﻿700 PEOF. T. G. BONNET AND MISS C. KAISIN ON THE [Nov. I905, 



ferrous oxide and the impossibility of getting the material quite pure. 

 The bulk-analyses are not unfrequent among serpentines. Dr. Hussak 

 also detected in theSprechenstein serpentine residual grains of sablite, 

 of a brownish diallage, talc (often associated with the latter), a 

 green chlorite and staurolite (in small round grains, or, more rarely, 

 as columnar crystals). He calls attention to slight differences 

 between the compact and the schistose serpentines, pointing out 

 that the former consist mainly of antigorite-scales, which are 

 arranged in two sets of parallel planes meeting at an angle of 

 90°, so as to produce a netting-like (gestrickte) structure. 'In 

 short, the sahlite-grains are related to the antigorite-serpentine, 

 exactly as the oli vine-grains to normal serpentine, and the horn- 

 blende-grains to the serpentine with lattice-structure/ So ' three 

 definite types of structure of genetic importance are now recog- 

 nized,' one of them being serpentine with netting-like structure 

 (gestrickte struktur)or augite (antigorite)-serpentine. 



One of us has, more than once, put on record his doubts of the 

 validity of this induction. 1 Dr. Teall himself expressed a suspicion 

 that the author had not made sufficient allowance for the effect of 

 mechanical disturbances. Prof. Eosenbusch 2 intimated in 1898 

 that the above generalization required some limitation, and Prof. G. 

 A. J. Cole 3 in 1902 cautioned the student against hasty recognition 

 of this netting-structure. 



The British-Museum. Collection of minerals contains a specimen 

 of antigorite from the Val Antigorio, a slice from which, by the 

 kindness of the authorities, has been cut for examination. It 

 was so ' flaky ' that the section had to be made parallel to the 

 cleavage, on which surface spots with a faint metallic gleam were 

 discernible, like the ghosts of enstatite. These could be distin- 

 guished under the microscope by a slight difference in structure 

 from the rest of the groundmass, which consisted of very minute 

 irregular flakes, with the usual bluish-white polarization-tints and 

 a slightly ' thorn-like ' aspect. No pleochroism is perceptible, and 

 this mineral (antigorite) is much less characteristic than in the 

 specimens from Sprechenstein. The most conspicuous objects in 

 the slice are a few little tufts of a fibrous mineral, like actinolite, 

 but with an extinction-angle ranging up to 35° (? woHastonite). 

 Three points are noteworthy in this type-specimen : one, the extreme 

 minuteness of the antigorite 4 ; another, that the rock has been 

 greatly affected by pressure ; and the third that it originally con- 

 tained, certainly enstatite, and so probably more olivine than augite. 5 



1 Quart. Journ. Geol. Soc. vol. lii (1896) p. 453 & ibid. vol. lix(1903) p. 59. 



2 ' Blemente der Gesteinslehre ' 1898, p. 525. 



3 ' Aids in Practical Geology ' 4th ed. (1902) pp. 149 & 180. 



4 To this I can find a parallel in more than one specimen from other localities 

 in my collection. [T. G. B.] 



5 F. Becke, in Tschermak's Min. & Petrogr. Mitth. n. s. vol. xiv (1894-95) 

 p. 271, describes the formation of antigorite in a rock which was substantially a 

 dunite, occurring near Windisch Matrei in the Stubachthal, and calls attention 

 to the frequent occurrence of the mineral in pressure-modified serpentines. 



