276 



sandstone appears a few yards below it, in the banks of the stream, 

 and also in a new road cutting close to the place. In Collin Glen, one 

 mile to the north of this, the chalk and the greensand are exposed in 

 the river, above the bridge, and there is also a band of a few feet thick 

 of lias under the mulatto stone. 



Examples of the conversion of chalk into granular marble, by the 

 contact of a whin dyke, maybe seen at the southern boundary of Bally- 

 murphy, three-quarters of a mile south of the White Eock Quarry, 

 "No. 5, in a ravine, to which the late Dr. Mac Donnell gave the name of 

 Allan's Ravine, in honor of a friend of his, a mineralogist, Mr. Allan, 

 of Edinburgh. The chalk is often altered as much as 8 or 10 feet 

 from the whin dyke, and it is altered in different degrees. In this one, 

 at Allan's Ravine, it is first coarsely crystalline next the trap, then 

 saccharine, then more loose and sandy-looking, then bluish gray, and 

 compact, and next common chalk. The altered chalk is phosphorescent 

 when heated. A mass of chalk inclosed in a whin dyke at Balmer's 

 Glen, ]N"o. 2, is altered in a similar way. So it is in a remarkable degree 

 in contact with the large columnar protrusion of trap, on the top of 

 Ballygalley Head, on the shore opposite to ~No. 12. At Glenarm there 

 is a singular compound dyke, consisting of three branches, which cuts 

 through the chalk, and includes masses of it, which are altered in a 

 similar way to that above described. 



5. The White Rock quarry, opposite to Belfast, is three miles north- 

 east of No. 4. The chalk here is 130 feet thick, and both the top and the 

 bottom of it are well exposed. The dip is 6° west, and as the face of the 

 rock slopes backward, an allowance for both slope and dip is made in 

 measuring the thickness. There is in this quarry a slip, or fault, with 

 a downthrow of about 30 feet to the south. The greensand here is 

 visible ; the upper part green sandy rock, with the usual fossils about 

 10 feet, then a buff- coloured, rather hard sandstone; 10 feet below, green 

 sandy rock again, about 10 feet; in all, 30 feet visible ; but- there may be 

 more visible under this, as the rock at the base is covered with rubbish 

 fallen from above. The greensand again appears in an old excavation, 

 about 12 chains north of this quarry. It is but a small pit, dug up as 

 " freestone," for scouring furniture by the country people. 



A mile to the south of the White Rock quarry, in Ballymoney, in 

 the face of a limestone quarry lately opened, there are four trap dykes in 

 about 30 yards of the length. One of them has a branch or fork (see 

 Fig. 2). To this fact, as well as to the five dykes mentioned at Augh- 

 nahough quarry (Eig. 1), I shall have occasion to refer in the sequel. 



6. Ballygomartin. There is nothing remarkable at this place. I 

 have put it as a locality into the table, chiefly to determine the thick- 

 ness of the trap in Divis mountain. 



The little table-land forming the summit of Divis mountain consists 

 of a beautiful clinkstone porphyry, of a reddish brown colour, containing 

 elongated lamellar crystals of glassy felspar, and concretions of bluish 

 white chalcedony. The rock is very sonorous, 



