of Derry and Antrim. £0$ 



Whoever has attended to the exertions of man when em- 

 ployed in altering our present surface, either by levelling 

 heights, or by making excavations, must nave observed that 

 it is the practice of the workmen to leave small cylindrical 

 portions standing, for the purpose of determining the height 

 of the old surface, and thereby ascertaining the quantity of 

 materials removed. 



To these may be compared the stratified basaltic hum-' 

 mocks so profusely scattered over our area, and which seem- 

 to show how high our quondam surface once reached. 



The hummock df Dunmull, three miles south-east from 

 Fortmsh, is very beautiful, it stands on the top of a high 

 ridge, and is a conspicuous object from all parts of the 

 country ; it is exactly circular, its flat surface contains art 

 acre, it is completely surrounded by a perpendicular fagade 

 about twenty-five feet high, and formed by two strata, a 

 columnar, and an irregular prismatic, resting upon it. 



From this elevated station, where I had the pleasure of 

 accompanying you, I showed you at six or seven miles di- 

 stance to the westward, among the Derry mountains, the 

 still loftier hummocks of Altabrian and Sconce, hemisphe- 

 rical in form, composed of but one stratum each, while their 

 swelling out bases displayed accumulations of many more: 

 and also near those the hummock of Fermayle, resembling 

 Dunmull^ but much larger, and also surrounded by a fa- 

 cade composed of tw-o strata. 



I showed you also at twenty miles distance to the south- 

 east, the gigantic Sltmish, one of our basaltic hummocks, 

 magnified (as it were) into a lofty and insulated mountain, 

 completely stratified from its base to its flat summit. 



I showed you likewise from the bottom of its ridge, the 

 neat but diminutive hummock, called the Rock of Clog her, 

 above Bushmills, As our time was precious, you took my 

 word for its stratification being precisely similar to that of 

 Dunmull. 



There are many other basaltic hummocks scattered over 

 the surface of our area, all of them either stratified or por- 

 tions of strata; two of the most remarkable are the hill of 



Knock 



