225 



pebbles, green sand, and numerous fragments of fossils. These re- 

 mains have nearly a vertical position when in situ, and Mr. Griffith 

 consequently infers that they are not in the position in which they 

 were deposited. 



The irregularities on the surface of the chalk are accurately filled 

 with the syenite : the chalk in immediate contact with the vein is 

 usually compact, sometimes crystallized ; and pebbles of quartz si- 

 milar to those in the green sand and chalk are found occasionally in 

 the syenite. The author noticed a small reniform mass of syenite 

 imbedded in the chalk — the grain of the included portion being finer 

 than that of the syenite in general. Small particles of chalk were 

 likewise noticed in the syenite, and the union of the two rocks is so 

 perfect that the chalk appears to be an integral portion of a compound 

 deposit. Among other peculiarities exhibited at the junction of the two 

 formations, the author mentions spheroidal masses of syenite in- 

 cludedin the chalk ; and, in conclusion, he says, that if the views which 

 he has put forward have been substantiated, a new and important fact 

 is added to those already described, which may ultimately lead us to 

 attribute a comparatively recent origin not only to syenite veins and 

 primary greenstone, but also to crystalline rocks generally when as- 

 sociated with schistose strata. 



A letter from H. T. De la Beche, Esq., addressed to the President, 

 and dated Truro, the 18th of December, 1835, was then read. 



This letter was accompanied by a collection of fossils from the 

 schistose rocks of the North of Cornwall, and presented to the Society 

 on the part of the Ordnance Geological Survey. 



Mr. De la Beche says that in the grauwacke of Western Somerset, 

 Devon, and Cornwall natural divisions may be made, founded on 

 marked characters. How far these divisions may coincide with those 

 in Prof. Sedgwick's Cambrian system he has no means at present of 

 judging ; but he is of opinion that the whole of the district is older 

 than the Silurian formations of Mr. Murchison. 



Some of the organic remains obtained at Dinas Cove, in Padstow 

 Harbour, belong to a system of beds consisting of slates, sandstones, 

 and conglomerates, which encircles the northern flank of Dartmoor, 

 then makes a great curve south of Launceston, bends afterwards 

 northward round the Rough Tor and Brown Willy granite, and lastly, 

 again inclines southward, crossing the Padstow river to the sea on the 

 western coast. In various parts of this line the system is fossiliferous, 

 particularly where limestone occurs or calcareous matter abounds. 

 The Tintagel slate, long since shown by Dr. Buckland and the Rev. 

 John Conybeare to contain organic remains, belongs to this system. 

 Part of the fossils which accompanied the letter were procured from 

 Trevelga Island (Lower St. Columb Porth), and Towan Head near 

 New Quay, from the same series of beds, which, in consequence of an 

 east and west anticlinal line ranging by St. Eval, St. Issey, and St. 

 Breocks Downs, is folded over to the south, and constitutes the 

 schistose system of St. Columb Major, St. Columb Minor, New 

 Quay, &c. 



