BASALT. 



303 



moles, projecting from the base of a stratified cliff, 

 about 400 feet in height: the principal mole is visible, 

 for about 300 yards in ex'ent, at low water, the others 

 not more than half that distance. It is composed of 

 polygonal pillars, of dark-coloured basalt, so closely 

 united, that it is difficult to insert more than a 

 knife-blade between them ; and the formation of a 

 continuous surface at each point in the pavement, by 

 polygons, whose angles vary considerably. Towards 

 the centre of the whole mass the pillars ascend ; and, 

 from the peculiar appearance of the surface, this 

 vertex is usually called the Honeycomb. The pillars 

 are irregular prisms of an uncertain number of sides, 

 varying from three to nine : there is one of three 

 sides near the centre of the Honeycomb, and several 

 of nine have been detected, but the hexagonal form 

 prevails most generally. 



Each pillar is in itself a distinct piece of workman- 

 ship ; it is separable from all the adjacent columns, 

 and then is itself separable into distinct joints, whose 

 articulation is as perfect as human exertion could 

 have formed them, the extremities of each joint being 

 concave or convex, which is determined by the ter- 

 minations of the joints with which it was united. 

 But there is no regularity as to the upper or lower 

 extremity being concave or convex ; the only law on 

 this point is, that the contiguous joints are, the one 

 concave, the other convex. In order to secure stabi- 

 lity to this piece of architecture, the angles of the in- 

 ferior joints frequently overlap those of the superior 

 so closely that the force required to dislocate them 

 occasionally fractures the joints. The geological 

 scenery east of the causeway is truly sublime : the 

 dark precipitous cliffs, which rise regularly in gradually 

 retiring strata, certainly suggests the idea of their 

 having been deposited age after age, as Werner 

 thought ; and the extraordinary appearance of the 

 various colonnades might, for a moment, seduce the 

 fancy of the visiter, and lead him to imagine that 

 here whole palaces had been overwhelmed in ruin. 

 These successive capes, which are visible from the 

 causeway, are but a part of one great headland, 

 called Benmore, the rival of Benmore or Fair- Head, 

 and all of them similarly formed. As an illus- 

 tration of this part of the basaltic coast of Antrim, we 

 may take a graphic sketch from the very remarkable 

 detached mass of Carrick-a-Rede. 



The island is nearly of the same elevation as the 

 adjacent mainland, rising about 350 feet from the 

 surface of the ocean ; and in the adjacent cliffs is a 

 very beautiful cave, about thirt feet in height, formed 



ntirely of columnar basalt, of which the bases ap- 

 pear to have been removed, so that the unsupported 

 polygonal columns compose the cave. Carrick-a- 

 Rede is separated from the coast by a chasm of sixty 

 feet in breadth. Vast iron rings are morticed into 

 the rocks on each side, to which are fastened two 

 ropes running parallel to each other, connected to- 

 gether with cross bars of rope at equal distances. A 

 series of planks are added ; and over this species of 

 primeval bridge, men, women, and children, are daily 

 in the habit of passing to the basaltic mass. 



Of the nature of the several mineral productions 

 to be found about the Causeway it may be said, that 

 where the basalt is not formed into columns, the 

 masses possess a considerable variety of texture as 

 well as colour ; in colour, they are to be found from 

 various shades of giey and brown to a dull red. All 

 these varieties are attributable to the iron contained 

 in the mass under various circumstances of chemical 

 influence. The basalt often approaches in its general 

 character to amygdaloid, the cavities being sometimes 

 very considerable, and either coated or filled entirely 

 with various minerals. In the former instance, the 

 interior surfaces have always a crystalline character, 

 which, when entire, not uncommonly constitutes a 

 hollow sphere, to which the name of Geode has been 

 applied. '\ his is principally the case with such as are 

 of a siliceous nature. Zeolite occurs here in every 

 known variety ; and that which is usually termed 

 fibrous, or mealy zeolite, is particularly deserving of 

 attention, from its extreme delicacy and brilliancy of 

 character, resembling the fine down of a thistle. 

 Calcareous spar is exceedingly common ; steatite and 

 green earth are occasionally found ; chalcedony, ap- 

 proaching to opal, and agates, are not rare. On the 

 side of Mount Pleaskin, or Placekin, near the Giant's 

 Causeway, there is a remarkable appearance of 

 imperfect crystallisation between the principal ranges 

 of pillars, much resembling the diverging figure of 

 radiated zeolite. The varieties of zeolite are well 

 known to abound in basaltic regions, particularly the 

 most northern, and that alluded to impresses the 

 idea of a rapid crystalline process. Intense cold and 

 frost most frequently produce a figure more or less 

 resembling it. 



On the islands of Staffa and Rathlin, curvilinear 

 prisms of basalt present themselves, which, as we 

 have already stated, much resemble the ribs of a 

 ship. Near the Cascade of Vestena, in the territory 

 of Verona, where a similar appearance exists, irre- 

 gular aggregated bodies (some approaching to a 

 sphere and some to an imperfect prism) rest within 

 the uppermost segment of the circle. The influence 

 of the laminated sphere seems no less applicable to 

 the various degrees of inclination exhibited by basaltic 

 columns in several other parts of the world. 



Great quantities of basalt are likewise found in the 

 vicinity of Mount Etna in Sicily, of Hecla in Iceland, 

 and of the volcano in the isle of Bourbon. These 

 three are the only active volcanoes in whose neigh- 

 bourhood it is to be met with ; but it is found adjacent 

 to many which are extinct, particularly the silent 

 craters of Italy. 



The rocks of the Cyclops, in the neighbourhood 

 of Etna, exhibit magnificent basaltic columns, which 

 at first view greatly resemble the Causeway pillars ; 

 but on a closer inspection, a very remarkable differ- 

 ence will be found to exist. The cyclopian pillars 

 are divided into distinct families or groups, of six or 



