﻿1850.] MURCHISON SLATY ROCKS OF THE SICHON. 



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those portions of it where the schists are less shivery, and where they 

 were formerly quarried for (imperfect) roofing slates — it seemed 

 hopeless to search for fossils. On one of the summits, however, 

 of the plateau on the right bank of the Sichon, and about two 

 miles to the south of the spot called the " Croix de Justice," I ob- 

 served courses of an earthy yellowish sandstone — not unlike some 

 British varieties of plutonic ash or volcanic grit — interlaminated with 

 the schists, in which I detected the remains of Encrinites. This 

 led me to re-examine on a subsequent occasion the schists of the 

 valley of the Sichon removed from the spots where they are most 

 interfered with by the porphyries, and by which in fact they have 

 in some places been so considerably metamorphosed as to part with 

 their lamination and become amorphous. On the right bank of the 

 stream, to the south of the abandoned " Ardoisiere," or slate quarry, 

 I further perceived highly inclined and vertical bands of pebbly con- 

 glomerate, subordinate to the schist. This pudding-stone contains 

 dark and light coloured, small, rounded pebbles of schist, quartz, and 

 a little limestone in a grey matrix, and might well pass for an inter- 

 calated conglomerate of the Silurian or Devonian systems. 



Taking simply into consideration the mineral structure of the slaty 

 schists, their purple plum-coloured exterior, and their fracture, com- 

 bined with the aspect of the sandstones, grits, and conglomerates, few 

 geologists, indeed, would hesitate to say that they formed part of what 

 was called the old greywacke series. This inference might be further 

 sustained by two courses of limestone which I discovered, the one of 

 two feet, the other of about nine feet in thickness ; this rock being 

 hard, of scaly fracture, and of light grey or bluish colour. 



Not far, however, from these calcareous courses I procured some 

 fossils, after a long search, in the thin layers of half-rotten, slightly 

 ferruginous schist. These having been subsequently examined at 

 Paris by M. de Verneuil, have proved to be — 



Productus fimhriatus, Sow., or a form with spines on the trans- 

 verse ribs undistinguishable from that species. 



Chonetes papilionaceal Phill. 



Orthis crenistria, Phill. 



Bivalve, resembling the Pleurophorus costatus, King. 

 Univalve shells in fragments. 



Phillipsia — i.e. the pointed buckler and cheek of this trilobite. 

 Encrinites of two species. \ 



Now (to say nothing of the carboniferous forms of Chonetes and 

 Orthis) as no spinose Productus like the P. fimhriatus, nor any 

 species of the genus Phillipsia, have ever yet been found in the Silu- 

 rian or Devonian systems, there can be no doubt that these schists of 

 the Sichon, ancient as they look, and as indeed they have hitherto 

 been considered, must now be viewed as really belonging to the car- 

 boniferous system ; and that the intrusive porphyries of this tract 

 were erupted after their deposition. 



Having thus satisfied myself concerning the rocks in the lower 

 part of the valley, I next sought to connect them with the higher 

 elevations of the chain of the Forez from which the river Sichon 



