278 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 13, 



much spoken of by Pilla and others, and having attracted the notice 

 of the geologists of the meeting at Florence, I visited* and made a 

 section of the strata which I now produce (fig. 34), as it differs 



Fig. 34. 



S.S.E 



N.N.W. 



Pieve a Settimo, 

 Valley of the Arno. 



Upper macigno 

 sandstone. 



Dome of alberese. 



essentially from those hitherto published f. It shows an underlying 

 light grey limestone or alberese, with fucoids followed by schists ; 

 next by the nummulitic limestone (y) ; and lastly by a vast over- 

 lying mass of macigno sandstone (</), as seen in the hills above St. 

 Martino. The lowest beds at the Calcinajo, to the south of Pieve-a- 

 Settimo, are thin-bedded, cream-coloured limestones (c??) of con- 

 choidal fracture, with marlstones which contain the Fucoides intri- 

 catus and F. TargioniX' These limestones, alternating with whitish 

 schists or marl, form a low dome, the south side of which dips under 

 other schists or shales of black and red colours, the "galestro" of 

 the natives {e), which are covered by a thin band of micaceous sand- 

 stone or macigno. Then come impure gritty light grey limestones 

 in strong beds of four to five feet thick (/'), which contain small 

 nummulites {N. globulus ?) and minute foraminifera, and towards their 

 upper portion pebbles of older compact limestone. These graduate 

 upwards into flaglike, sandy, impure limestone of a bluish tint, which 

 forms the passage into a great and distinctly overlying mass of 

 *' macigno" {g). Beds of coarse grit or small conglomerate occur 

 near the base of the sandstones, in which are pebbles of quartz and 

 diallage, and above them are small micaceous sandstones, which, 

 although weathering yellowish, are of the usual grey macigno colours 

 when freshly quarried. Some of these masses assume spheroidal 

 shapes, and there are other alternations of similar sandstones and 

 shale, and coarse grits (conglomerates, &c.), which occupy the sum- 

 mits of the adjacent hills. Now, all these beds are perfectly con- 

 formable, and from below the village of St. Martino to the tops of the 

 hills they dip to the S.S.E. at angles gradually decreasing from 20° 

 to 10°. It is thus seen, that the nummulites occurring in the lower 

 part of all the macigno which is here exposed, are clearly covered by 

 another and much greater mass of macigno. These strata are there- 

 fore, according to my view, on the very same parallel as the nummulitic 

 and flysch group of the Alps. 



The hills near Pistoja, and, in short, everywhere around the vale 



* I was kindly accompanied by the Marchese Carlo Torrigiani and Professor Tar- 

 gioni-Tozzetti. 



t Compare my section with that of Pilla in his work, entitled " Distinzione del 

 Terreno Etruri tra' piani seoondari del mezzo-giorno di Europa-" Pisa, 1816. 

 Tav. iii. fig. 3 ; and Mem. Soc. Geol. Fr. vol. ii. 2nd ser. p. 103. 



X Where these limestones are of a bluish-grey colour they are called " Colom- 

 bino," as distinguished from the whiter beds or " alberese." 



