ox A PIECE OF TIMBEli, ENCEUSTED WITH LIME. 89 



facing the picturesque Barrasford Crags southwards and about a 

 mile distant. These crags form part of the Great Basaltic Whin 

 Sill that can be traced with occasional breaks from Kyloe Crags 

 in the north to Glenwhelt in the south-west of JSTorthumberland. 

 A considerable depth of Boulder-clay is left here above the strata, 

 through which the colliery had been sunk in 1865. In the new 

 pit opened last year, about two hundred yards north-eastward, 

 the depth of the clay is given as forty-four feet, an upper band 

 of limestone occurring at eighty feet from the surface, only six 

 inches thick, while a lower band, two feet and a half thick, is 

 ninety-six feet fi'om the surface. 



At the request of my friend, the late Mr. George Tate, F.G.S., 

 after a visit to Birtley in 1867, I obtained from Mr. Armstrong 

 a section of the strata in his pit, which seems to be approximately 

 correct. It is as follows : — 



FEET, 



Clay 24 



Freestone 22 



Plate 14 



Freestone 20 



^Limestone 4 



Freestone 10 



Plate 12 



Coal 2 



The new colliery, closely adjacent to this older one, is, accord- 

 ing to Mr. Armstrong, twenty fathoms and a half deep, and in 

 it the limestones arc two, instead of one as in the disused pit, 

 though both together do not equal in thickness the single band 

 of the latter by twelve inches. 



The plank or board itself is six feet eight inches in length, two 

 inches and a half thick, and five inches in breadth, a portion, one- 

 third, of which is now shown. f The laminated, compact deposit 

 of crystalline carbonate of lime that has been gradually formed in 

 eleven years is from one-eighth to a quarter of an inch in thickness. 

 Oa this particular board about three-sixteenths has been formed, 



* Mr. Armstrong describes it as a coarse bund above, blue in tho centre, and with shale 

 intermixed. The limcslonc strata have a thitkncss of thirty-livo to forty feet, at a maxi- 

 mum, near Scwinj,' Shields, but varies {rreatly in the district. 



t It may be seen in tlie Natural History Museum. 



