1G8 Dr. Berger on the Geological Features 



Along the western escarpment of the basaltic mountains in Lon- 

 donderry, the mulattoe is seen underlying the chalk in Kedy 

 Donald and Ballyness hills. Between Ballyness and Benbradagh, at 

 the head of the vale of the Kelvin river, a wild circus opens, barred 

 on the north by basaltic ridges, and having the insulated primitive 

 district of Coolcroscrahan on the south ; the Glen Ullin water and 

 Donavenny brook rise also within the area, and^flowing in a direc- 

 tion contrary to that of the Kelvin, join the Aghivey river itself, 

 tributary to the Bann. Within this area a remarkable bed of marie 

 occurs, which is mentioned here, on account of its containing nu- 

 merous green particles ; but it differs so essentially from the Mu- 

 lattoe in its chemical composition, containing only one-fiftieth of 

 calcareous matter, that it cannot with propriety, though resembling 

 it in external appearance, be considered as the same rock : the base 

 is a soft clay, greyish, with a slight red tinge ; the structure 

 is thin slaty j it contains some small worn quartz pebbles : the chalk 

 has not yet been traced in this district, but along the banks of 

 Donavenny brook, a breccia formed of chalk flints, imbedded in a 

 calcareous cement, and underlying the basalt, seems to indicate 

 its proximity. This breccia is probably connected with the aggre- 

 gation of flints, usually interposed between the basalt and chalk, 

 as described in the next article. 



The subjoined list of the organic remains occurring in the Mu- 

 lattoe of Ireland, will be found to agree closely with those pre- 

 sented by the green sand in England. 



