THE 



GEOLOGICAL MAGAZINE. 



No. L.— AUGUST, 1868. 



I. — The Chalk of Antrim. 

 By J. Beete Jukes, M.A., F.R.S., &c. &c. 



MOST geologists are aware that the Chalk of Antrim, although 

 full of flints and fossils like those in the English Chalk, is a 

 hard splintery limestone, known here as the '^ White Limestone." 

 Its induration is often attributed to the action of the basaltic cover- 

 ing which spreads over it, and the coincidence of the two things is 

 certainly remarkable ; but I think I can now show that they are 

 not connected in the way of cause and effect. 



The upper surface of the Antrim Chalk is frequently, perhaps 

 always, covered with a layer of flint gravel, from one or two to six 

 feet in thickness, often filling up small hollows in the surface of the 

 Chalk. Over this comes the basaltic mass, commonly composed of 

 thick ranges of columnar basalt, each range resting on, and covered 

 by, amygdaloidal beds, which often exhibit a rude lamination or 

 stratification that may perhaps indicate the lines of flow. Thin beds 

 of clay with lignite and iron-ore occur occasionally between the 

 basaltic seams. 



It is remarkable that the flints in the flint-gravel which lies be- 

 tween the Basalt and the top of the Chalk, are often, when broken 

 open, found to exhibit concentric bands of various tints of red sur- 

 rounding a grey interior, and coated by an external white coat ; the 

 latter appearing to be due to weathering after the red tints were 

 acquired. 



I had been inclined on previous visits to Antrim to attribute this 

 reddening of the interior of the flints, in the gravel between the 

 Basalt and the Chalk, to the igneous action of the former upon them. 

 A recent observation, however, made while inspecting the work of 

 Mr. Du Noyer, and our two new assistants, Messrs. Warren and 

 W. B. Leonard, has led me to doubt even this. 



At a quarry (known as McGarry's quarry), about three or four 



VOL. V. — NO. L. 23 



