J. A. Birds — Geology of the Channel Islands. 81 



rather one or two bands of schistose strata which make their appear- 

 ance in Kocquaine Bay, Guernsey ; and, again, the schists or shales of 

 Jersey. 



In the former case the rocks are of a bluish-grey colour, weather- 

 ing brown, and have at first sight a general Silurian or Devonian 

 aspect. They are referred to by Prof. Ansted in a note concerning 

 the absence of any deposits in Guernsey more recent than the fun- 

 damental syenites and gneiss: "A small patch of clayslate," he says, 

 "in Eocquaine Bay is hardly an exception." 



This so-called patch (where I examined it) consists of two or 

 three bands of slate, which are imbedded in the midst of a felspathic 

 syenite, and dip at a very high angle to the east. I traced them 

 for about fifty or sixty yai'ds on the land side of the fort called 

 Rocquaine Castle till they became lost under the sea. Probably, at 

 low water, they may be found in other parts of the bay. The cavities 

 left by decomposed felspar have often a very deceptive resemblance 

 to casts of Brachiopoda, and to encrinital remains ; but I searched in 

 vain for any trace of fossils. Possibly these may yet be discovered. 

 Should this not be the case, the schists will not, of course, yield 

 any evidence of their age, or of that of the felspathic and horn- 

 blendic rocks amid which they lie. In a mineralogical point of 

 view, however, they would still be interesting, as showing a stage 

 in the progress of metamorphism, viz. a passage from sedimentary 

 schists into a greenish-grey porphyritic rock containing crystals of 

 felspar and calcite (?). 



Alderney, according to Ansted,^ besides the portion of sandstone 

 above referred to, consists entirely of syenite, with the exception of 

 a single boss of hornblendic porphyry, upon which Fort Touraille is 

 erected. Ortach and the Casquets, although few, if any, geologists 

 have landed to examine them, are believed to consist of similar 

 syenite or porphyry with cappings of the same sandstone as 

 Alderney. It is said that the syenite enters and pierces the sandstone 

 in the Casquets — a very important point — but one which requires 

 confirmation. 



Of Guernsey I can speak from personal observation. It is di- 

 visible geologically into two or three very unequal portions by a 

 line drawn N.W. from some quarries just above St. John's Church, 

 in the town of St. Peter, to some other quarries below Capelles 

 School ; and thence again S.W. to a quarry on the right or north 

 side of the Cobo Eoad, close to Cobo Bay. About three-quarters, or 

 rather four-fifths, of the island south of this line consists of a very 

 felspathic syenite and gneiss, and the remaining quarter or fifth of a 

 hornblendic ' granital ' — a compound of quartz and hornblende. A 

 third division consists of a syenite often charged with specks and 

 flakes of mica. This micaceous sj^enite may be traced along the 

 coast from near the centre of Cobo Bay and Grandes Rocques almost 

 to Fort Doyle, at the north-eastern extremity of the island. In 

 the centre of Grand Havre, however, and on Mont Cuet — between 

 Grand Havre and Lancresse Bay — and perhaps at some other points 

 1 The Channel Islands, p. 268. 



DECADE II. VOL. V. — NO, II. 6 



