138 Dr. Berger on the Geological Features 



sides of the channel of the Roe, as is the case at the romantic 

 waterfall called the Dogsleap, near Newton, where a fine natural 

 section of that rock is displayed, and lower down the river in the deer 

 park of Mr. M'Causland ; from the district of Tamna Arran near the 

 head of the valley of the Roe, the boundary passes along the Douglas 

 river, a branch of the Mayowla to its confluence : thence it sweeps 

 to the east of the Cairns of Slieve Gallion, and near the confines of 

 Moneymore and Lissane, towards the sources of the Ballinderry 

 river, in the north-east of Tyrone. 



A little to the north-east of the source of the Roe, and almo* 

 surrounded by the secondary and basaltic ridges of Benbradagh and 

 Cragnashoack, we are surprized at meeting with a small insulated 

 district of mica slate ; it forms the entire mass of the mountain of 

 Coolcoscrahan, which rises nearly 1300 feet above the level of the 

 sea. 



The characters of the mica slate vary much less than might be 

 expected, considering the extent it occupies in the north of Ire- 

 land ; upwards of two-thirds of it belong to the talcky variety, 

 the remainder to the common, or that which contains the least 

 quantity of mica and the greatest of quartz. 



A circumstance rather remarkable is, that, amongst the multi- 

 plicity of specimens I have examined, I do not remember one that 

 contained garnets. How far that extensive formation of mica slate 

 may be metalliferous, it is impossible to say in a country hitherto so 

 little explored. 



The subordinate rocks which not unfrequently occur in the mica 

 'slate, shall be noticed separately. 



