Geological Society of London. 237 



The northern part, low ground with hummocks, consists principally 

 of a group of crystalline or subcrystalline rocks, in constitution 

 diorites or syenites. They are described by Ansted as sedimentary 

 rocks metamorphosed into syenites ; but they show no bedding 

 either in the many quarries, or, in general, in the shore outcrops, 

 nor do their varieties occur in any manner indicating an order of 

 succession. They appear at Castle Cornet to meet the gneiss in- 

 trusiyely, and their microscopic structure is igneous. A remarkable 

 appearance of bedded structure at Fort Doyle is the only strong- 

 argument for a metamorphic origin, and this may be explained as a 

 caught-up mass in conjunction with crushing-planes. The author 

 therefore regards them as igneous. 



An oval area between St. Sampson's and St. Peter's Port is occu- 

 pied by hornblendic rocks, locally called "birdseye," which may be 

 described as hornblende-gabbros. These also have been called meta- 

 morphic. They too, at Hogue-a-la-Perre and at another point, present 

 appearances of bedding ; but on the same general grounds as for 

 the preceding group, these also are regarded as igneous. 



Two granitic masses are described : the coarse pink granite of 

 Cobo, on the west coast, and the finer-grained grey granite weather- 

 ing pink of Lancresse, oh the north. Each is seen to intrude : the 

 Cobo granite into gneiss at Hommet Barracks ; the Lancresse granite 

 into diorite at Fort le Marchant. Besides these are some smaller 

 masses. 



Dykes are remarkably abundant and various. Granites and elvans 

 are plentiful everywhere ; felsites very rare. The majority of the 

 dykes are diorites, varying in coarseness and often of enormous size ; 

 there is also mica-trap. In some of these dykes a cleavage has 

 been developed, so that some resemble slates. Infiltration veins are 

 abundant. 



In relative age the gneiss appears to be the oldest rock, the 

 hornblende-gabbro to be next, then comes the diorite group, while 

 the granites are newer still. Of the dykes the newest are the coni- 

 pactest diorites. As to the absolute geological age of the rocks 

 no satisfactory evidence at present is known ; it will have to be 

 sought for in the other islands and in France. 



2. " On a New Specimen of Megalichthys from the Yorkshire Coal- 

 field." By Prof. L. C Miall, F.O.S. 



A large and unusually complete example of this fish was recently 

 found in the roof of the Halifax Hard bed, at Mr. S. B. Ellison's 

 Firebrick works. Idle, near Leeds. The fossil is in good preserva- 

 tion, the ventral surface is uppermost, the pectoral, ventral, anal, 

 caudal fins can be more or less satisfactorily made out ; the dorsal 

 surface is absent. The length is 3 feet 8^ inches, of which the head 

 measures about 10 inches, and the tail (from the end of which 5 or 

 6 inches may be wanting) about a foot. Judging by the large skull 

 figured by Agassiz and preserved in the Leeds Museum, Megalich- 

 tlujs may have attained a length of from 4 to 5 feet. 



The skull shows the mandible and mandibular teeth, the end of 

 the snout, the opercula, and the jugular plates. The pectoral fins 



