164 M. Brongniart on the position 



2dly. The calcareous sandstone formation (terrain calca- 

 reo-psammitique ; the arenaria, &c. of the Italian geologists. 



3dly. The serpentine formation (terrain ophiolitique). 



I mention the tertiary formation in this communication 

 solely to shew that it is not forgotten ; but as it hears do 

 direct relation to the serpentine formation, the principal 

 object of this paper, I shall not here speak of it. 



There are some other rocks or formations, either subor- 

 dinate to these, or in an independent position, such as the 

 gypsum and saline formations. Those of marble or crystal- 

 line limestone, which I equally pass over in silence, either 

 because they are foreign to my subject, or because I am not 

 exactly acquainted with their relations, or lastly, because 

 I have nothing more to say concerning them than has been 

 published by Italian naturalists. 



I confine myself therefore to the examination of the rela- 

 tive position of the serpentine with the calcareo-sandstone 

 formations, and I ought, consistently with the principles I 

 have above laid down, previously to determine, with the 

 greatest possible exactitude, the rocks composing these for- 

 mations. 



1. The calcareo-sandstone forms, in this part of the 

 Apennines, the principal mass of the mountains, and may 

 be considered as the base or fundamental formation. It is 

 composed of the following rocks. 



a. A calcareous micaceous sandstone ; that is to say, a 

 rock apparently arenaceous, but solid and even compact, and 

 hard enough to strike fire with a stroke of the hammer; 

 more or less mixed with mica, and often traversed by veins 

 of calcareous spar ; its predominant colour is blueish grey 

 with a crust of reddish brown (pietra serena of the Floren- 

 tines). (Mountain of Fiesole near Florence; Oneille; 

 Barigazzo.) 



b. A micaceous sandstone (macigno and bardellone, 

 Brocchi), passing into schistose sandstone and even a spang- 

 led (paillete) argillaceous slate alternating with them (Doc- 

 cia; Arezzo; Fiesole). 



