180 Dr. Berger on the Geological Features 



The above table will convey an accurate idea of the general 

 configuration of the circumference of the basaltic area. 



The aggregate mass of all the formations constituting the third 

 system of mountains, appears to form a species of basin of which the 

 lowest point is situated near the center of the valley of the Ban ; hence 

 they rise, towards the south-east, where they lean against the exterior 

 chains of the Down mountains ; towards the north-east, where the 

 primitive rocks of Cushleak emerge ; and towards the south-west* 

 where they abut on the great central chain of Londonderry. In this 

 last direction, all the strata attain their greatest height, the chalk 

 standing in Slieve Gallion at 1460 feet and upwards, and the basalt 

 in Cragnashoack at 1864 feet. It is rather remarkable that the cap 

 of basalt grows gradually thinner in proceeding towards the same 

 point. On the north-east edge of this basin, the inferior limit of 

 the basalt, or its junction with the chalk, is 500 feet lower, but the 

 thickness of the cap of trap, increasing in the inverse ratio of this 

 diminution of level, raises the summit of Knocklead till it nearly 

 rivals Cragnashoack. In the south-east border, at Cave hill, the line 

 of junction is about 200 feet lower than in Knocklead ; the cap of 

 trap is there very thin, but in the adjacent summit of Divis nearly 

 equals in thickness that which covers Knocklead. At Divis the line 

 of junction is depressed 200 feet below the level which it occupies 

 at Cave hill. 



The high chains which form the borders of this basin on the east 

 and west, present a far less rapid slope towards its interior than 

 towards its circumference. 



Thus between the towns of Belfast and Antrim, the watershed or 

 highest point of the road which there crosses the eastern chain, is 

 situated three miles and a half from Belfast, and eight miles and a 

 half from Antrim, at the elevation of £)97i feet above the level of 



