1837.] 



through the Northern Circan 



and the conglomerate rock results from its detritus. At Nullacherla, 

 the blocks were little above the soil, and situated in the same position 

 as those of conglomerate sandstone, evidently forming a bed in the 

 last mentioned rock. The third kind of laterite, that at the summit of 

 the hill of Bimlipatam, overlaying, and imbedding fragments of, gneiss, 

 both at the surface and near the points of contact with the subjacent 

 rock, contains many veins of hsematitic iron of different thickness, into 

 which it passes in its lower part. Those blocks called laterite at Pud- 

 dagarum are, evidently, in appearance, and in the circumstance of as- 

 sociation with the heematitic iron ore, analogous to that of the Neil- 

 gherries ; of the other two, w 7 e must be satisfied of their similitude, by 

 induction only. 



Adverting to the rarity of contorted strata in the rock prevailing in 

 this part of India, namely, gametic gneiss, with occasional intermix- 

 ture of albite ; and to their frequency in the other variety of the analo- 

 gous rock, containing mica, in many other localities, we must feel 

 anxious to inquire, what is the real cause of the difference in the forms 

 assumed by the strata, when in a semi-consolidated state. 



Along the route which we have travelled, the only two places, where 

 I met with gneiss whose strata were contorted and undulating, were 

 the hill of Bezoara, and that about two miles west of Cottipollium. 

 We must not omit mentioning, that, in both places, the disturbance did 

 not extend far; at Bezoara it occupied only one side of the hill; and 

 in that near Cottipollium, the contortions were seen only in loose, 

 erratic blocks, perched on the south declivity of the hill. It is neces- 

 sary here to remark that, through the Bezoara strata, were seen large 

 dykes, or beds, of greenstone, which, evidently, must have contributed 

 greatly to the distortion of the strata. 



The other variety of gneiss, containing mica, such as that in the 

 table-land of Mysore, and elsewhere, is traversed by numerous basaltic 

 or porphyritic dykes, the existence of which suggests a plausible reason 

 for the disturbed strata of gneiss in that district. 



Thus, suppose two enormous dykes of basalt, at a certain distance 

 from each other, bursting through the semi-consolidated, horizontal 

 strata of a rock, say gneiss, enclosing between them a certain extent of 

 these strata, which, we suppose, to be under a moderate pressure from 

 above : what will be the consequence of a force, such as that of the 

 intruding basalt, applied on the extremities of the strata, in opposite 

 directions ? 



The luminous experiment of Sir James Hall, answers satisfactorily 

 this question. He put on a table different coloured square pieces of 

 - cloth, horizontally, one over the other, having put a board with a mode- 

 rate weight on them (PI. 17- fig- 10) : « a, are the pieces of cloth, 

 which, in the beginning of the experiment, were horizontal; b the 



