96 Mr. N, J. Winch on the Geology of 



large crystals of greenish white felspar. Blocks of it are found in 

 the bed of the Deals water at Dilston near to Hexham, 



Blocks of porphyry slate are found on the banks of the Tyne near 

 to Horsley, and masses of the same rock, including small red garnets, 

 in the bed of the Deals water. 



Masses of fine-grained granite appear on the surface over the 

 whole country. Those from the banks of the Tees and other parts- 

 of the south of Durham consist of small grains of white quartz, 

 black mica, and flesh-coloured felspar. 



Considerable quantities of marl have been discovered on the 

 west side of the river Till in situations which seem to have been the 

 bottoms of lakes ; and in this alluvial matter horns of some species 

 of bos and cervus are found imbedded. The marl is of a light grey 

 colour, and contains bivalve and univalve shells which retain their 

 pearly lustre. This substance has been noticed at Wark, Sunnylaws, 

 Learmouth, Mindrum, the Hagg, the Hopper, and at several other 

 places in that neighbourhood. It probably rests in some places on 

 the beds that I have described as prevailing on the banks of the 

 Tweed, and at others on porphyry or grey-wacke. 



j The following passage should have appeared in the paper after the account of 

 the Walker dyke at page 22.] 



The next basaltic dyke worthy of notice is one which, passing 

 from west to east under Tynemouth Priory may be seen to divide 

 the strata at the south-east point of Prior's haven, where it forms a 

 wall 12 feet broad in the cliff and in the rocks below. A vein or 

 fissure 12 inches in breadth and filled with tufaceous matter inter- 

 sects the dyke from top to bottom near its center, and the basalt 

 strongly resembles the Coley Hill stone. ■ - 



