ROCKS OF THE CHANNEL ISLANDS. 33 



and dark grey layers, the latter being of a coarser texture 

 than the others. No fossils have been found in it, but ripple 

 marks are seen on the surface of some of the beds. This 

 rock has been identified with the " Schistes de Saint L6," 

 which cover considerable areas in Normandy and Brittany. 

 These " Schistes " are considered by French geologists to be 

 the basement beds of the Cambrian system, but as they have 

 hitherto proved unfossiliferous, they have been thought by 

 some to be Pre-Cambrian or Archaean. In France they are 

 said to rest on gneiss or other unquestionably Archaean rocks 

 with which, however, they have nothing in common. In 

 Jersey, the Argillite cannot, I think, be seen to rest on the 

 Archaean diorite previously referred to, as in every locality 

 I have examined granite intervenes, which granite is intrusive 

 both in the diorite and Argillite. M. Noury, it is true, who 

 considers the diorite to be of Cambrian age, believes it to be 

 intrusive in the Argillite, but does not point out any positive 

 proofs. That the Argillite is of more recent date than the 

 diorite appears to me almost certain, but it is unquestionably 

 older than all the remaining rocks of Jersey. The Argillite is 

 hardened and altered in colour at its contact with the granite, 

 but nothing resembling mica schist occurs. The rock called 

 Claystone or Felspar porphyry occurs in various localities in 

 Jersey, and is considered by several geologists to be an altered 

 form of the Argillite. Such is also my opinion, and the 

 probable cause, I think, is the eruption of the quartz felsite 

 or rhyolite, although some portions of the (presumably) 

 altered Argillite are at a considerable distance from the 

 visible portions of the quartz felsite. There is no Argillite in 

 Guernsey. M. Noury is mistaken in referring the Schistose 

 Eock, near Pleinmont, to this formation. It is an intrusive 

 dyke of very considerable width, and has a Schistose struc- 

 ture agreeing in direction with the foliation of the adjacent 

 gneiss. 



The next younger rock in Jersey is the granite already 

 mentioned as intruding in the diorite and Argillite.* It also 

 occasionally contains inclusions of these rocks. This rock 

 has been referred to by Ansted and others as syenite, but as 

 this term is now restricted to rocks in which quartz is either 



* I have followed M. Noury on making the granite anterior to the Rhyolites 

 but I an not sure this is correct. The absence from the Rhyolites of diabase 

 veins, so numerous in the granite, is in favour of this view, but on the west of 

 Fremont Point the granite is seen to intrude into a quartz felsite, which I con- 

 sider belongs to the Rbyolite series, and if so the granite must be posterior to the 

 older Rhyolites at least. M. Noury, without referring to the intrusion, mentions 

 the rock in which it occurs and styles it a curite. He does not include it among 

 the rhyolites, and considers it a modified argillite. 



