82 



Mr. N. J. Winch on the Geology of 



About thirty years since a brine spring was discovered at Birtley 

 colliery 76 fathoms below the surface, in driving a water level through 

 a slip of 4^ fathoms throw. The spring being found to produce 

 26400 gallons of water in twenty-four hours, extensive salt works 

 were erected on the spot, which are still carried on with success. 

 Within 50 or 60 yards north of the slip, from which the spring 

 issues, the Birtley dyke before mentioned crosses the strata from east 

 to west, casting up the coal measures on the northern side 29 fathoms ; 

 and the slip having a south-eastern direction probably meets the 

 dyke and is a branch from it. The water level is driven in a bed of 

 blue shale containing ironstone in beds and in nodules. The ana- 

 lysis of the water by Mr. G. Woods is as follows. * 

 Contents in 1000 grains of water. grains. 



Dry muriate of soda .... 87 



Dry muriate of lime .... 43 



Muriate of magnesia 



Carbonate of lime 



Carbonate of iron 



Silica .... 



131 



A little carbonic acid gas. 



Before the publication of Camden's Britannia in 1607, a brine 

 spring had been observed to issue from the rocky bed of the Wear 

 at Salt water Haugh near Butterby; for in that work it is first 

 mentioned. In 1684, Mr. Hugh Todd drew up an account of this 



* The carbonates, small as is their proportion, are sufficient to make the water appear 

 turbid, when viewed in the large reservoirs at Birtley. They are very readily thrown 

 down by the addition of quick-lime, and this method of purifying the solution is always 

 pursued in that salt-work. The brine leaves no incrustation upon the evaporating pans. 



