466 PROF. T. G. BONNEY AND MAJOR-GEN. C. A. M'^MAHON 



characteristics similar to those of the Lizard from some variety of 

 peridotite may now be regarded as demonstrated to the satisfaction 

 of all petrologists who have studied the rock in the field and with 

 the microscope. It is of course true that other magnesian silicates, 

 such as rhombic and some monoclinic pyroxenes, can produce ser- 

 pentine ; but the correspondence between rocks thus originated and 

 those of which the Lizard serpentine is a type, it' it exist in certain 

 rare cases, is almost exclusively in chemical composition and is 

 associated with marked diversity in other respects. 



The Lizard serpentines can be roughly separated into two groups : 

 in the one a foliated mineral of the enstatite group is a conspicuous 

 accessory ; in the other a colourless augite or hornblende, usually 

 the latter. A few are non-porphyritic, and in some cases exhibit 

 no certain traces of any pyroxenic mineral, rhombic or monoclinic, 

 though of course a spineliid or some iron oxide is always to be 

 detected, and in one instance (at the Rill, W. of Kynance CoYe)the 

 presence of a fair proportion of felspar has been asserted. 



Of the tables annexed, one gives the mineral, the other the 

 chemical composition of certain varieties of the serpentine. Chryso- 

 tile is almost always present as well as ordinary serpentine, so it has 

 been thought needless to enumerate these separately. The more or 

 less foliated enstatite (bronzite) is also more or less serpentinized ; 

 in most cases, if not all, it is probably bastite, as has been demon- 

 strated by Mr. Teall *. The hornblende (except when specified) is a 

 white variety ; the iron oxide is generally magnetite, but in the red 

 serpentines much hematite is present. The term "spineliid " includes 

 all varieties, from those which are a very deep brown (barely 

 translucent), probably chromite, to the translucent rich brown 

 grains (picotite) present in several specimens f. Under the head 

 " chlorite" is placed a colourless mica-like mineral, resembling that 

 described by Herr Weigand t- In §ome cases the included opacite 

 suggests that it may be a bleached biotite. The figures within 

 brackets in the column headed "liemarks '' indicate the number of 

 specimens on which the result is founded. The localities are 

 arranged in order, beginning at the south end of the east coast and 

 going round from the north to the west coast, which is followed 

 southwards. 



The annexed table of analyses contains, we believe, all that have 

 been published, with four others, which, by the kindness of Prof. 

 W. Eamsay, F.E.S., have been made in the chemical laboratory at 

 University College (London). Eor these the authors are indebted 

 to Mr. M. W. Travers, to whom they tender their best thanks. 

 Numbers I.-Y. doubtless represent varieties of the serpentine with 

 conspicuous crystals of enstatite (bastite), chiefly used for orna- 

 mental purposes; YI.-IX. are from varieties of the PorthaUa 

 serpentine ; X., XI. are varieties of the dull-coloured compact 



* ' Brit. Petrogr.' p. 88. 



t See also ' Picotite in Serpentine,' H. Fox, Trans. Eoyal Geol. See. Corn- 

 wall, Tol. xi. pt. 5 (1891) p. 33Q. 



I Quoted by Mr. Teall, 'Brit. Petrogr.' p. 112. 



