264 



A. McKenry — TracJiytic Roclis of Antrim. 



Figs. 5 and 6 are ideal sections, showing the probable conditions 

 before and after the Upper Basaltic period. 



Fis:. 0. 



Ideal section showing probable mode of intrusion of the trachyte through 

 Chalk and Lower Basalt. 



1. Chalk with eroded surface. 2. Flint-gravel bed, composed of burnt chalk 

 flints, chalk fragments, and red marly clay. 3. Lower Basalt. 4. Trachyte 

 (laccolite) . 



Subsequent to ray discoveries in county Antrim and, in the same 

 year, when engaged in some work in the Mourne Mountain district, 

 county Down, I was struck with certain similarities between the 

 granite of this area and the acid rocks of county Antrim ; namely, 



Fi-. 6. 



Ideal section showing probable position of the (rocks) pisolitic iron- ore, trachyte 

 gravel, and Upper Basalt, over the trachyte and Lower Basalt. 



1. Chalk. 2. Gravel bed. 3. Lower Basalt. 4. Trachyte. 5. Horizon of 

 denudation, along which were deposited the pisolitic iron-ore bed, trachyte 

 conglomerate and sand, basaltic and ferruginous conglomerates, marls, and bole, 

 containing plant ajid other remains. 6. Upper Basalt. 



that the Mourne granite is often very trachytic in appearance, 

 frequently resembling some of the varieties of the Tardree rock. It 

 also cuts off basalt dykes, which are most probably of the Lower 

 Basaltic series, and is itself, as well as these dykes, invaded and cut 

 up by later basalts. Besides, there is a strong and most suggestive 

 link between the rocks of the two areas (Antrim and Down) in the 

 trachyte porphyry mass that occurs half-way between them, near 

 Hillsborough, county Down. It is therefore highly probable that 

 the Mourne granite is of Tertiary age. 



