THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



MARCH 1892. 



XXIV. Petrological Notes on the Euphotide or Saussurite- 

 smaragdite Gabbro of the Saasthal. By Professor T. Gr. 

 Bonney, D.Sc, LL.D., F.R.S., fyc* 



EVERY geologist has heard of, many have seen, the 

 erratics of this peculiar variety of euphotide, which are 

 so abundant in the upper part of the Saasthal, and are more 

 sparingly distributed over the southern portion of the Swiss 

 lowland. But though they have been noticed by some foreign 

 authors f, and are frequently mentioned by English J, the only 

 attempt at a complete history of them in our language is to be 

 found in a brief abstract of a paper by Captain Marshall Hall § . 

 The author, however, was not very successful in obtaining 

 good specimens and was unable to arrive at any very definite 

 conclusions, so that some account of my own examination 

 may be useful, at any rate to English students. 



* Communicated by the Author. 



f E. g. at some length by R. Hagge, Mikroscop. Untersuch. iib. Gabbro 

 u. verw. Gesteine. Referred to briefly by Rosenbusch, Mikrosk. Physio- 

 graphen, s. v. Gabbro. 



\ " Contributions to the History of Euphotide and Saussurite " 

 (T. S terry Hunt, Amer. Journ. Sci. xxvii. p. 336, 1859) contains a number 

 of historical references, and gives the result of a chemical and mineralo- 

 gical investigation of this group of rocks. But as it is founded on a 

 study of hand-specimens only, and these were not examined with the 

 microscope, some of the conclusions appear to me to hold good only in a 

 mineralogical, not in a petrological sense. 



§ Mineralogical Magazine, vol. v. p. 194. 



Phil. Mag. S. 5. Vol. 33. No. 202. March 1892. S 



