of the rocks that I have seen intersected, with some additional localities.
| Rocks cut by Dykes. | Localities. |
| Primitive limestone | Vide former list. |
| Sienite | Newry, Bloody Farland, &c. |
| Slaty quartz | Farland point, Donegal |
| Mica slate | Kildrim lead mine in Donegal |
| Gneiss | |
| Transition limestone[1] | Blockhouse Isle, entrance of Carlingford bay. |
| Old red sandstone | Near Newton Glens. |
| Flœtz limestone alternating with sandstone and underlying the coal | East of Bally-castle |
| Coal measures | East of Bally-castle |
| Chalk | East of Glenarm, where the limestone is rendered hard and crystalline in contact with the dykes. One of the dykes branches and encloses portions of the limestone, and many other places, see page 172. |
| Flœtz trap, basalt[2] | Giant's Causeway, and many other places. |
The induration which the secondary rocks undergo when traversed by dykes has often been noticed; it is not my intention now to discuss this subject; I shall only mention that the induration does not extend far from the dyke, and that the phenomena though very frequent are not universal.[3] I have only noticed one instance of remarkable change in a primitive rock contiguous to a dyke. In the case I allude to, viz. in the lead mine of Kildrim in the county of Donegal, mica slate adjacent to the dyke had its texture quite loosened, and was in a dusty state.
- ↑ A dyke also traverses transition limestone, containing magnesia limestone, at Scarlet point in the Isle of Man.
- ↑ Inserted by the Editor
- ↑ The white limestone when thus indurated becomes, as is well known, phosphorescent. I have found limestone, accompanying the undoubted lavas of Andernach in the Palatinate, and containing garnets and augite, not to possess this property.
