B A S A L T. 



bonato of barytcs. Some of the salts of barytes are 

 violent and certain poisons, destroying animals by 

 inflamhu; the intestines, mid are often used for the 

 destruction of vermin. 



301 



Sparry Mr.-yti-s. 



The barytes, of which we give a representa- 

 tion in the above figure, is usually divided into 

 a variety of sub-species, they are not, however, of 

 sufficient general interest to be separately enumerated, 

 The radiated heavy spar is remarkably phos- 

 phorescent when heated. This property was first 

 observed in the year 1630, by a shoemaker, named 

 Vincenzo Casciarolo, during his search after the phi- 

 losopher's stone. When the mineral is calcined, 

 pulverised, and made into cakes, it acquires a strong 

 phosphorescent property by exposure to light ; the 

 phosphorescence is visible, upon taking it into a dark 

 place. When rendered phosphorescent it is known 

 under the name of Bolognian phosphorus. 



It may be proper to state that the columnar heavy 

 spar has been frequently confounded with white-lead 

 Sjtar, but is distinguished from that mineral by the 

 following characters : white lead spar has an adaman- 

 tine lustre, its fracture is conchoidal, and its specific 

 gravity rather more than six ; whereas columnar 

 heavy spar has a pearly lustre, distinct cleavage, and 

 a specific gravity of less than live. See CELESTINE, 

 STRONTIANITE, and WITHERITE. 



BASALT. A term employed by geologists to 

 describe a rocky compound, which furnishes some of 

 the largest and most beautiful columnar masses which 

 are to be found in the whole structure of our globe. 

 Natural architectural edifices of this description are 

 now existing, which far exceed in magnitude the 

 Titan grandeur of Egyptian art ; and it is gratifyin^ 

 to know that some of the most beautiful specimens of 

 these temples, reared by the Creator as illustrations of 

 his power, are found within the circle of the British 

 isles. The singular tendency which basaltic formations 

 evince to assume a columnar form, is familiar to the 

 commonest observer : and no constituent material of 

 the solid globe has more frequently been an object ol 

 geological speculation in recent times ; theorists ot 

 nearly equal ingenuity having contended as vehe- 

 mently for its igneous as its aqueous origin. 



Although various parts of Europe and Asia abound 

 with examples of basaltic columns, yet the island ol 

 Staffa and the Giant's Causeway appear to be the 

 most extensive and striking in the known world. It is 

 extraordinary that the former should scarcely have 

 been known previous to the year 1 772, when it was 

 admirably described by sir Joseph Banks, on his 



visit to the Scottish Hebrides. The latter was better 



wn by the previous description of the bishop of 

 Ossory. 



The island of Staffa will, in the first instance, en- 

 gage our attention ; and its extraordinary basaltic 

 characteristics have been so accurately described by 

 Dr. Macculloch as to render any further comment 

 superfluous. The principal beauties of Staffa are to 

 be found on its iron-bound coast, and our plate, IU- 

 SALTES, will serve to convey a good notion of the 

 character of one of its greatest basaltic ornaments. 



If we commence with the landing place, the columns 

 in this quarter are placed in the most irregular direc- 

 tions, being oblique, erect, horizontal, and sometimes 

 curved; while they are also far less decided in their 

 forms than the larger vertical ones which constitute 

 the great race. When they reach the grassy surface 

 of the island, they gradually disappear ; " but are 

 sometimes laid bare, so as to present the appearance 

 of a geometrical pavement, where their ends are to 

 l)e seen ; in other places displaying portions of their 

 parallel sides. 



At the Scallop, or Clamshell Cave, the columns o. 

 one side are bent, so as to form a series of ribs not 

 unlike an inside view of the timbers of a ship. The 

 opposite wall is formed by the ends of columns, bear- 

 ing a general resemblance to the surface of a honey- 

 comb. This cave is thirty feet in height, and sixteen 

 or eighteen in breadth at the entrance : its length 

 being 130 feet, and the lateral dimensions gradually 

 contracting to its termination. The inside is unin- 

 teresting. The noted rock Buachaille, or the herds- 

 man, is a coniadal pile of columns, about thirty feet 

 high, lying on a bed of curved horizontal ones, visi- 

 ble only at low-water. The causeway here presents 

 an extensive surface, which terminates in a long pro- 

 jecting point at the eastern side of the great cave. It 

 is formed of the broken ends of columns, once conti- 

 nuous to the height of the cliffs. This alone exceeds 

 the Giant's Causeway, as well in dimensions as in the 

 picturesque diversity of its surface ; but it is almost 

 neglected among the more striking and splendid 

 objects by which it is accompanied. The great face 

 is formed of three distinct beds of rock, of unequal 

 thickness, inclined towards the east at an angle of 

 about nine degrees. The lowest is a rude trap tufa, 

 the middle one is divided into columns placed verti- 

 cally to the planes of the bed, and the uppermost is 

 an irregular mixture of small columns and shapeless 

 rock. The thickness of the lowest bed at the western 

 side is about fifty feet ; but, in consequence of the 

 inclination, it disappears under the sea, not far west- 

 ward of the great cave. The columnar bed is of 

 unequal depth ; being only thirty-six feet at the 

 western side, and fifty-four where the water first pre- 

 vents its foundation from being further seen. To the 

 eastward its thickness is concealed by the causeway. 

 Thus, at the entrance of the Great Cave on this side, 

 the columns are only eighteen feet high, becoming 

 gradually reduced to two or three, till they disappear. 

 The inequality of the upper bed produces the irre- 

 gular outline of the island. The inclination of the 

 columns to the horizon, in consequence of their verti- 

 cal position towards the inclined plane of the bed, 

 produces a very unpleasing effect whenever it is 

 seen from the south-west : the inclination of 

 nine degrees conveying the impression of a fabric 

 tottering, and about to fall. Fortunately, the most 

 numerous and interesting views are found in positions 



