338 



On the Geology of Cutch. 



sand, and scorise in very thin laminae. Below the columnar basalt is a 

 bed of a friable variety, three feet in thickness. In some parts the 

 columns are capped with a thin band of ironstone. The interior of this 

 crater is about 80 yards in diameter, and consists of volcanic sand, with 

 imbedded angular fragments of basalt. The most perfect of these cra- 

 ters, or circular spaces, are generally hid from view, being approachable 

 only by the narrow ravine forming the outlet of the watercourse which 

 cuts through them. The basalt varies greatly in texture and general ap- 

 pearance : in some places it is columnar, exceedingly hard and compact, 

 in others it contains imbedded crystals of felspar, and it occasionally pre- 

 sents the structure and texture of an amygdaloidal clay. Some varieties 

 also consist of concentric layers of a kind of brittle, clayey substance, 

 inclosing a nucleus of hard rock ; the whole being imbedded in a mass 

 of clay, which looks as if a number of small roots were entwined about 

 it. All the varieties are frequently found in the same bank or hillock. 



Several other small basins have been blown out in the surrounding 

 table-land, forming inverted cones, about 15 or 20 feet in depth ; and 

 are composed of the same materials as those just described. Many of 

 them consist entirely of small, brittle particles, of a pale yellow colour, 

 evidently sulphuric. The clay has, in various places, been burnt into a 

 perfect brick ; and the marls, or sandy clays, are frequently of a beautiful 

 bright purple. Quantities of talc, or mica, lie scattered about, twisted 

 and contorted into a variety of shapes ; and some of the iron ore which 

 covers the surface, appears to have been partially fused, consisting of a 

 spongy, vesicular mass. The whole has the appearance of having been 

 for some time subjected to considerable heat, and then suddenly blown 

 up. The cones and banks of loose volcanic scoriae must be yearly wash- 

 ing away ; and it is difficult to conceive, that the walls of solid basalt 

 forming the sides of the craters, can belong to a similar period, having 

 all the appearance and texture of very old basalt ; but it is possible that 

 a recent eruption may have taken place in the site of one of a more anci- 

 ent date, thus presenting a mixture of old and recent volcanic products. 

 If it is true, that basalt owes its columnar structure to its cooling slowly 

 under a great pressure, it is impossible that these masses of columnar 

 basalt and the loose cones of scoriae can be contemporaneous. 



In the nummulitic marl forming the banks of a river which flows past 

 this patch of blown-up ground, is a stratum of earth containing small 

 nodules or rounded masses, of a pale yellow colour, translucent and^ 

 brittle, and which burn with a bright flame, giving out a strong aromatic 

 odour. It is contained in a dry, olive-brown earth, so light as to float 

 in water. 



