170 M.Brohghiart on the posilion 



precise acceptation of that term, nor even an argillaceons 

 schist, as it might at first sight be considered : for argilla- 

 ceous schist, and above all that considered as primitive or 

 even transition, is generally hard, of a fine and close grain, 

 and often shining ; if it contains mica, it is as it were dis- 

 solved and not in distinct plates. The schistose rock that 

 occurs here beneath the jasper, possesses nearly the opposite 

 characters, it is so earthy and easily broken, that a speci- 

 men of a certain size cannot be obtained. It is either of a 

 dull yellowish, greyish, or even nearly blackish colour. The 

 mica when met with, which is but very rarely, is seen dis- 

 seminated in small spangles, difficult to be observed, and 

 that which completes the series of its difiFerences, is that vt 

 effervesces strongly with nitric acid. 



This rock, when homogenous, is then a greyish marly 

 schist, such as I have characterized it in my mineralogy, and 

 when it contains mica, it is exactly referable to that which I 

 have elsewhere * named dull micaceous argillaceous slate 

 (phillade micacee terne). 



This marly schist passes into compact limestone by insen- 

 sible gradations, and alternates with beds of a fine compact 

 limestone, of a smoke grey colour, and of a clean conchoidal 

 fracture, traversed by numerous veins of calcareous spar. 



The immediate and evident superposition cannot then here 

 be doubted of the serpentine, of the diallage rock, rocks so 

 clearly crystallized, and jasper on calcareous rocks which 

 offer all the characters of a deposit (d'un sediment). 



Before I quit this example and the place that furnished it, 

 I ought to state some other facts that will complete its 

 history. 



While mounting up the Montenero or the mountain of 

 Silva, and traversing the Col of Beverone, in order to pass 

 by Garbuglaria into a valley which joins the valley of the 

 Varra at Madrignano, the jasper formation is constantly on 

 the right, that is towards the East, here rising towards the 



* Mineralogical classification of mixed rocks, Journal des Mines, vol. 

 xxxiv. p. 5. &c. 



