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speculate why it is a good road metal lying on the chalk in one quarry, 

 and worthless as such lying on it in another, when we consider that the 

 rock at both places has the same component parts ; but even here, as I 

 have stated, without comparing two quarries four miles asunder, a hard 

 layer lies over, and in contact with a soft one, in the same quarry. 



In another quarry here, about a furlong north of the road, near a 

 small house at Aughnahough (Fig. 1 ), there are five whin dykes, cutting- 

 through the chalk, which have left their mark in a singular way. At 

 one side of every dyke there is a wall-like mass of altered chalk, standing 

 upright in the quarry, from 5 to 1 0 feet in height, and 1 8 inches to 

 2 feet thick. The quarrymen did not remove these walls, as they 

 consist of dolomite, and are not fit for lime. Some of it is phos- 

 phorescent when heated. The ordinary chalk was excavated from 

 between the dykes, and carried away, and, as just stated, the wall-like 

 masses left standing. The black trap has been decomposed, and fell away 

 from about them. The limestone quarries here have nine or ten whin 

 dykes visible ; but those five, in the short space of a few yards, suggest 

 the idea that the trap of Antrim came up through fissures, and there 

 appears to be plenty of them for the purpose of eruption. They are 

 usually from 5 to 10 feet thick. There is no greensand visible in 

 any of these quarries. Its place is at the bottom of the limestone, 

 which has never been worked through. Between the two quarries on 

 the north side of the road there is a downthrow to the north of about 

 30 feet. 



Fig. 1. 



Whin Dykes and Pillars of Dolomite in Chalk at Aughnahough. 



4. Ballycollin. The quarry here is called Collin Well Quarry. It 

 affords a pretty large supply of limestone to the country over the 

 mountains westward, towards Glenavy and Crumlin. The limestone 

 here measures 50 feet in thickness, but the bottom is not satisfactorily 

 seen, and it has a dip west of 10°, so that it may be 60 or 70 feet. The 

 greensand is visible in the stream adjacent, and it measures there about 

 35 feet thick. About nine-tenths of it here is calcareous matter. The 

 contact of the greensand with the underlying rock is not clear, but red 



