INTRODUCTION. xxv 



of Belfast and Strangford Loughs, and again at Greencastle, on the 

 extreme south of the county. These, with the addition of two little 

 specks of Permian, and frequent deposits of Boulder Clay and superficial 

 drift, complete the geological series as exposed in County Down. 



The most striking feature in the geology of Antrim is the enormous 

 mass of volcanic rock which covers almost the entire county. This great 

 sheet of basalt has been erupted through wide fissures, now fiUed with 

 hard rock, and known as dykes. The trap, or basalt, extends into Deny, 

 and has a combined area, in the two counties, of some 1,200 square miles, 

 with a thickness of more than 1,000 feet in some places. An interesting 

 series of sedimentary rocks of ^Lezozoic age are developed in the county, 

 and by their contrasts of colour heighten the picturesque beauty of the 

 fine sea- cliffs for which Antrim is famous. These rocks consist of Chalk, 

 Greensand, Liassic, and Triassic strata ; but as they have been universally 

 covered by the Trap, and are only seen in slight exposures where the 

 igneous rock has been denuded away, they have but a subordinate 

 influence on the native vegetation. 



The county of Derry is separated by its geology into two distinct 

 regions ; the east side being part of the great basaltic plateau of Antrim, 

 with the same imderlying series of sedimentary strata, though the latter 

 are more sparingly developed. 



The hiUs in this part of the county are of trap, which decomposes with 

 comparative facility, yielding a rich, loamy soil, and a native vegetation 

 of considerable variety. To the west of the basaltic escarpments there 

 are occasional bands of limestone, of tri%dal importance, and gi-anite rocks 

 are rare. Sandstones, however, some of mezozoic and others of palaeozoic 

 age, are developed to a considerable extent, mainly towards the centre of 

 the coimty. Further west there appear great masses of Mica, Schist, or 

 other Metamorphic and crystalline rocks, monopolising the entire 

 surface. They cross the western and northwestern boundary, and 

 constitute a characteristic feature in the geology of the neighbouring 

 counties of Donegal and Tyrone. The weathering of these silicious rocks 

 proceeds slowly, and the result of their disintegration is a less valuable 

 soil, and a flora comparatively poor. 



Over the entire region the Glacial Drift has been more or less spread, 

 being seen especially in the valleys, and along the lower slopes of the 

 hiUs. The Boulder Clay, as distinguished from moraine matter, is a 

 marine deposit composed of fine tenacious clay, with which is intermixed 

 an abundance of stones of various sizes, from a few grains up to many 

 tons in weight. This drift largely influences vegetation, and is of the 

 greatest importance to the tiller of the soil. The effect of its absence may 

 be noted by the traveller on the railway Kne between Comber and Cross- 

 gar. On much of the ground passed over the drift is absent, and the 

 treeless rocky surface seems as unprofitable to the fanner as it is 

 uninviting to the botanist. Esker mounds, and local beds of gravel, are 

 not uncommon, but their influence on the vegetation is not extensive. 



