I36 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [May 1 894, 



regarded as primarily due to pressure operating upon suitable 

 materials, the structure of others seemed opposed to this explanation • 

 but, whatever the genesis of these rocks, they are rightly called 

 Archaean gneisses and schists. 



Simultaneously with the last paper appeared one by Mr. Hill 

 on the Rocks of Sark, Herm, and Jethou. The greater part of the 

 island of Sark consists of dark hornblendic banded rocks, which 

 closely resemble those of the Lizard. Owing to certain appear- 

 ances, which he describes, the Author at that time concluded that 

 these rocks originated through some kind of successive deposition, 

 if not actually from aqueous sedimentation. He thus sums up what 

 appears to have been the order of geological events : — A mass of 

 Archaean rock of uncertain origin (the Creux-Harbour gneiss) had 

 deposited on it a thick series of beds of alternating materials, 

 principally hornblendic, possibly of volcanic origin. Over these a 

 mass of granitic or syenitic igneous rock subsequently flowed. 

 After the solidification of this, but still probably at a very early 

 period, came a great east-and-west nip. Except certain intrusive 

 dykes there are no later materials with which to continue the history 

 of Sark. Mr. Hill further insists upon the Archaean age of these 

 rocks being analogous to rocks elsewhere admittedly pre-Cambrian. 

 They seem distinctly older, he says, than the unfossiliferous argillites 

 of Jersey, themselves of extreme antiquity. Some of the views 

 expressed in this paper have been materially modified quite recently, 

 but before considering these matters it will be convenient to pro- 

 ceed with Mr. Hill's next paper on the Channel Islands. 



This relates to the rocks of Alderney and the Casquets. Alderney 

 itself consists for the most part of crystalline igneous rocks, to 

 which the name of granite may be applied. The general appear- 

 ance of this is said to recall the diorites and syenites of Guernsey, 

 but the abundance of mica and the smaller amount of hornblende 

 connect it rather with the granites of Jethou and Sark. The 

 minor intrusives are next described, one of the most interesting 

 being a dark noncrystalline rock of high specific gravity, approaching 

 somewhat near to a picrite — the first instance known to Mr. Hill in 

 these islands of an olivine-bearing rock. 



The grits constitute an important formation, which may be traced 

 at intervals from the Casquets on the extreme west to a point east 

 of Cherbourg — a distance of 30 miles. The Author remarks that 

 the current-bedding, arkose materials, and sporadic pebbles, point 

 to the immediate neighbourhood of a coast similar to the present 



