368 Prof. T. G. Bonney — Ligurian and Tuscan Serpentines. 



feet, reach quarries in this rock, some of considerable size. The 

 gabbro is coarsely crystalline, consisting of plagioclase felspar (re- 

 sembling labradorite), partly of a dull bluish colour, partly changed 

 into white " saussurite " and greenish dial! age, with a rather silvery 

 lustre, the crystals commonly varying from ^ " to § " diameter, and 

 some dull green spots possibly denoting altered olivine. The slide, 

 however, which I have had prepared, does not show any of the last, 

 but consists of plagioclase felspar more or less altered, diallage, 

 ordinary augite, and a little secondary hornblende. 1 The rock is 

 locally known as pietra di macchina, and is quarried for mill-stones. 

 It varies a little in the relative amount of diallage and felspar and 

 evenness of crystallization, but is, on the whole, very uniform in 

 character. I had not time to trace out its limits, but the size of 

 the mass must be considerable. 



Bearing away to the right and slightly ascending, we approached 

 the serpentine, which forms hereabouts the upper part of the hill. 

 The actual junction of the two rocks is obscured by vegetation, 

 soil, and detritus, but in a water-course I obtained a fair section, 

 which satisfied me that the gabbro was intrusive in the serpentine. 

 Quarries in the latter rock are still more numerous than in the 

 former, so that, though all the natural surfaces are much decomposed, 

 there is no difficulty in obtaining a good supply of specimens. 



The general character of the serpentine appeared to be very 

 uniform — a ground-mass of a dull purple with a tinge of green 

 irregularly mottled by the latter colour; in this are scattered rather 

 small crystals of a greenish mineral resembling enstatite. Thin 

 veins of green steatite are not unfrequent. After long exposure the 

 rock becomes of a pale grey green. It is sharply but irregularly 

 jointed, the joints often coated with a film of white steatite, and 

 sometimes becoming brown by exposure. In general character the 

 rock is identical with those already described and with that of the 

 Lizard, so that, from examination in the field alone, one might fairly 

 claim for them a similar origin. A microscopic slide shows no 

 unchanged olivine, but in parts, as in the last described, a structure is 

 visible indicating that this serpentine also is an altered olivine rock. 

 I do not find any unaltered enstatite or augite, but several grains 

 resembling the talcose mineral described above. In another slide, 

 cut some years since from a specimen purchased in Florence, the 

 enstatite still shows faint tints and a little of the serpentine in the 

 ' strings ' exhibits slight chromatic polarization. 



On returning from the quarries I descended into the glen above 

 Figline, and a short distance from the latter found stratified rock by 

 the road-side. This at first was an argillaceous rock, with concre- 

 tions, looking as if it had been much crushed. A little nearer occurs 

 a harder, bedded rock, bands of which have a flinty texture and 

 fracture of a dull reddish colour. 2 The peculiar sharp jointing, baked 



1 An analysis of the diallage is given by D'Achiardi, vol. ii. p. 84, and of the 

 felspar (labradorite), id. p. 104. The rock is commonly called '•granitone" by 

 Italian geologists. 



2 I believe this is the " gabbro rosso " of some authors. 



