m 



On the Geological characters of the 



[July 



above, and sometimes has a bluish tinge (No. 3). Frequently it pre- 

 sents varieties, being either finer or coarser grained (Nos. 4 and 5). 

 The quartz is very abundant ; the lithornargic earth scanty, and the 

 mica is met with in small disseminated scales, " few and far between." 

 The original sand-stone rock, then, of which these nodules are frag- 

 ments, must have resulted from the fracture and disintegration of some 

 still more ancient crystallized rocks. The sandstone, thus formed, be- 

 ing, in its turn, disrupted, the fragments were tossed and rolled about by 

 some aqueous catastrophe, until they became embedded in this laterite 

 (so called), or conglomerate rock which we now see. This view of the 

 case, indicates violent disturbing forces, occurring at two distinct periods 

 of time. Besides the sand-stone, fra gments of ochrey iron ore, to be 

 hereafter mentioned, were found imbedded in the clay. 



I was unable to trace the appearance of stratification elsewhere 

 than in this nullah. The ground rises abruptly from its banks to the 

 N. W., forming one of the eminences bounding the lake on that side, 

 and the rock changes character from what I have described above, as 

 occurring in the bed of the nullah. Instead of seeing merely the sand- 

 stone nodules embedded in clay, we have a rock possessing the more 

 characteristic qualities of laterite (No. 6). It is rendered cavernous 

 by tortuous cavities, which penetrate it in all directions, sometimes 

 filled with red or yellow ochraceous earth ; sometimes with a white 

 clay, like decomposed felspar ; but frequently they are quite empty, 

 which is caused, it appears to me, by water percolating from above, 

 carrying with it the soft substance of these earths, the spaces they 

 once filled being thus rendered void (No. 7). 



This laterite still shows evident traces of the sand-stone, describe d as 

 found, in such large fragments, imbedded in the walls of the nullah ; 

 but the pieces are much rounded and comminuted, and are united 

 together by a very compact, heterogeneous, kind of paste, composed 

 apparently of the debris of the sandstone itself, of iron ores and of the 

 lithomargic earth. There is no mistaking the sand stone, which may 

 be picked out, in pieces of the size of a walnut, from the centre of a 

 mass of the laterite, and clearly shews the same structure as that of 

 the nullah (No. 28). 



Pebbles, of various kinds of crystallized rocks, are met with, imbedded 

 in the hardest and most compact laterite. On the rising grounds to the 

 north of the lake, I picked out fragments of white quartz rock, some 

 pieces angular, others much rounded (No. 9) ; of very compact siliceous 

 sand-stone, of a red colour, so hard as to be broken difficultly with a 

 heavy hammer (No. 10), and of a white, granular, friable, disintegrat- 

 ing sand-stone (No. II.). Added to these, a great profusion of frag- 

 ments of ochrey iron ore, red and brown (No. 12 and 13), a good deal 



