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



In the Mineralogical Museum at Florence, Professor Grattarolo (to 

 whom I am much indebted for information on localities, etc.), 

 showed me a collection of serpentine and gahbro from Impruneta, 

 a few miles from the city. These had the same general character 

 as the above ; but both rocks were much decomposed, so that, on 

 hearing there were no excavations, I did not think it worth while 

 visiting the locality, as I probably should not have been able to 

 learn more than I could from the specimens. 



These serpentines, then, and no doubt several other isolated 

 patches in the Ligurian Apennines, which I had not the opportunity 

 of visiting, must be added to the rapidly increasing group of altered 

 olivine rocks, primarily of igneous origin. To these also belong, as 

 I have already pointed out, the serpentines of Elba, and in our own 

 country those of the Lizard, Ayrshire, Portsoy, with other parts of 

 Scotland ; and — as I shall show on a future occasion — of North 

 Wales. To these also must be added some of the Alpine serpentines. 

 Here, however, careful discrimination will be needed, for though no 

 doubt true serpentine is present in the Alps, some of the rocks com- 

 monly mapped under that name have received it improperly, being 

 only serpentinous, i.e. rocks into whose composition other minerals 

 enter very largely, and in many cases simply serpentinous schists. 



Further, it is impossible to avoid being struck with the frequent 

 association of serpentine and gabbro ; at these four localities in 

 Italy, the two extremes being a good hundred and twenty miles 

 apart (and I believe in several others), at the Lizard in Cornwall, 

 and on the coast of Ayrshire — to speak only of those which I have 

 myself visited, we have gabbro intrusive in serpentine. This can 

 hardly be a mere coincidence. These gabbros also are remarkably 

 like one another in aspect. Some observers, indeed, have asserted 

 that the serpentine is the result of transmutation of a gabbro. Now 

 that the microscope is used in petrology, I do not think we 

 shall hear much more of that statement, which in many cases was 

 founded only on very hasty examination in the field, and has seldom 

 a better base than the fact that serpentine is one of those minerals 

 which, like some people, can make a great show with but little means. 

 It is often instructive to see how "serpentinous" a rock will appear 

 to the eye, which, on careful examination, proves to be mainly com- 

 posed of other minerals. Keflection, too, should have suggested to 

 petrologists that felspar is not an easy mineral to remove from a rock. 

 The case of greissen, tourmaline-rock, etc., may, I am aware, be 

 quoted ; but these are always comparatively local, while in the case 

 of serpentine we should have to pseudomorphose masses of gabbro 

 containing billions and billions of cubic yards so perfectly that no 

 trace of the felspar remained, and by so strange an agent that its 

 action is found to have stopped abruptly. The representatives, then, 

 of altered olivine-gabbros, will be found in the troktolite group ; 

 and where gabbro and pure serpentine (i.e. a rock the ground-mass 

 of which consists almost entirely of hydrous silicate of magnesia 

 with some oxides of iron) are associated, the two rocks are of inde- 

 pendent origin. It will be well for travellers to observe carefully 



