HAMILTON ON THE GEOLOGY OF TUSCANY. 291 



posed igneous influence, the beds lose their former character ; the 

 shales become more marly and laminated, and the harder beds 

 have a less cherty appearance. It is remarkable, considering the 

 intensity of the agent which must have caused the change, to what 

 a short distance it seems to have extended ; for on descending the 

 ravine, about 100 yards further, I came upon the secondary indu- 

 rated marls, perfectly unaltered, of a grey white colour, resembling 

 those near the Certosa at Florence and at Castiglion Fiorentino on 

 the road to Cortona ; and a little way further, the alberese or 

 scaglia limestone is also seen unaltered, but dipping considerably 

 to the S. S. AY. Here then we have a key to the whole metamor- 

 phic formation, which is derived from the altered marls and sand- 

 stones (macigno) of the secondary or Apennine formation, acted 

 on by the protrusion of the igneous rocks of the ophiolitic or 

 serpentine class, which are found in the immediate neighbourhood. 

 The passage of the red gabbro into the half altered beds of 

 stratified sandstone and marl, I subsequently found in several 

 other localities round this central mass, particularly on the road 

 from La Cava to Monte Catini, where the contortions of the strata 

 are well exposed, and are really deserving of notice from their 

 extraordinary convolutions. Here, too, in a direct line from the 

 summit of the Poggio alia Croce to Monte Catini, a gradual passage 

 may be traced to the unaltered shales, limestone, and macigno. 



C. Igneous Rocks. 

 These appear to me to belong to three distinct periods : : 



1. Serpentine, or ophiolitic rocks (Trap of secondary period),. 



2. Selagite of Monte Catini (Trachyte of tertiary period). 



3. Basalt of Radicofani (Recent). 



1 . Serpentine. 



This rock is developed in many parts of the western portion of 

 the Tuscan States. The principal localities where I had an oppor- 

 tunity of observing it, are at the copper mines of La Cava, and along 

 the chain of hills extending from Monte Catini to Castellina, includ- 

 ing Monte Miemo. To the south of the Cecina, it bursts forth 

 at Monte Libbiano, where it rises to a considerable height — at 

 Monte Rufoli, where it covers an extent of many miles — at Monte 

 Cerboli — Rocca Sillana and Monte Castelli — all belonging to the 

 same system. Near Florence it also shows itself in two spots, LTm- 

 pruneta and Prato, the latter of which I did not visit. It varies 

 considerably in its appearance, character, and hardness, its chief 

 permanent characteristics being its green colour and its soapy feel. 



At Monte Catini the rock is soft and soapy, occasionally contain- 

 ing portions of a harder nature. It is of a uniform greyish-green 

 colour, without the white spots which give to that of Psato, LTm- 

 pruneta, and Monte Rufoli its peculiar character, resembling the 

 serpentine of antiquity. It here derives its principal interest 

 from the copper mines with which it is associated. The copper 

 ore, which is exceedingly rich, occurs in irregular veins and 



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