346 



Jukes — On the Chalk of Antrim. 



miles W.N.W. of Lisburn, we observed the facts indicated in tlie 



diagram below : — 



4. 



, 



■" 



■ 



= 







— 



^ 



■ — ' 



"\ 



J 



^ 





3.^^^ 



mm 



m 



w 



■ 



■ 





<9 .; 



■ 



i 





Diagram-section, McGarry's Quarry, "W.N.W. of Lisbum, Co. Antrim. 

 4. Columnar Basalt getting platy below. 3. Clay and Lignite, or Culm. 



2. Flint gravel, the flints generally reddened internally. 1. Chalk with grey flints. 



The Chalk showed a total thickness of about forty feet, and dipped 

 westerly at about 10°, the green " Mulatto stone" appearing from 

 underneath it at the eastern corner of the quarry. The Chalk has 

 the usual covering of flint gravel, which in some places attains a 

 thickness of three or four feet. Over this was a layer of dark clay, 

 like a coarse under-clay of the Coal-measures, showing a platy 

 lamination in the part exposed to the air, but being quite soft and 

 unctuous when dug into for a few inches. In the upper part of 

 this was a band, three or four inches thick, of a kind of lignite, 

 sometimes more like culm in some parts, splitting into cubical 

 pieces with a bright face like some coals. Over this came coarsely 

 columnar basalt, of which a thickness of thirty feet was shown in 

 one part of the quarry. The lower foot or two of this basalt showed 

 a tendency to split into rough flaggy slabs, but the rest was rudely 

 columnar with a few irregular cross-joints. 



The lignite often showed a distinct woody fibre, in the pieces of 

 two or three inches in length, which we procured ; but the work- 

 men told us they often got flattened stems of trees, two or three feet 

 long. 



In the loM^er part of the soft clay I got a flint, the size of the 

 fist, which, on being broken, showed the usual concentric red- 

 tinted coats in its interior. 



The only legitimate deduction from these facts seems to me to 

 be, that if the superincumbent basalt did not by its transmitted 

 heat indurate the clay and alter the lignite immediately below it, it 

 could not affect the flints in the flint-gravel under that clay, still 

 less the mass of the Chalk under the gravel. 



The effects of the numerous dykes and veins of igneous rock in 

 this country, on the rocks they pass through, are often very obvious, 

 but rarely extend for more than a few feet from the walls of the 

 intrusive masses. 



I may add that on another day during a visit to the hills on the 

 north of the town of Antrim, I was struck with the resemblance 



