230 



Dr. Berger on the Dykes 



of the rocks that I have seen intersected, with some additional 

 locaUties. 



Rocks cut by Dykes. 



Localities. 



Primitive limestone 



Sienite 



Vide former list. 

 Newry, Bloody Farland, &c. 

 Farland point, Donegal. 

 Kildrim lead mine in Donegal. 



Blockhouse Isle, entrance of Carlingford bay. 

 Near Newton Glens. 



East of Bally-castle. 

 Fast of Bally-castle. 



Slaty quartz 



Mica, slate ......... 



Gneiss ••• 



Transition limestone * 



Old red sandstone 



Floetz limestone alternating with 



sandstone and underlying the coal. 



C!oal inP3siires ........ 



Chalk 



East of Glenaim, where the limestone is ren- 

 dered hard and crj-stalline in contact with 

 the dykes. One of the dykes branches and 

 encloses portions of the limestone, and 

 many other places, see page 172. 



Giant's Causeway, and many other places. 



Floetz trap, basalt+ 



The induration which the secondary rocks undergo when tra- 

 versed 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.:]: 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 magnesian limestone, at Scarlet 

 point in tlio Isle of Man. + Inserted by the Editor, 



i The white limestone when thus indurated becomes, as is well known, phospliorescent. 

 I have found limestone, accompanying the undoubted lavas of Andernach in the Palatinate, 

 and containing garnets and augite, not to possess this property. 



