CHAP. 1.] THE KADAPAH FORMATION. 129 
however, there is apparently a marked general undulation in the eastern 
N. S. undulation due Cf Mountain region which seems to have been 
fo original form of floor. | originally given to the lie of the strata by the 
irregular form of the floor of the basin over which they were deposited ; for 
the lower groups rise up to the surface and form the higher ranges of the 
Nullamullays in the northern part of the area, while the great group of 
the Cumbums forms the larger part of the hilly country to the south, 
as in the eastern water-basins of the Penn-air and Chey-air. 
The lie of the slates and quartzites in this mountain region, 
DIOE idol undulations, especially towards the north, 1s characterized by 
i Ome: very peculiar ellipsoidal undulations ; the largest 
of these is the great mountain mass of the Eeshwarnacoopum,* where 
the strata are lying up the sides and cropping out round the base of the 
mountain like the coats of a great onion. In Mr. Foote’s descrip- 
tions it will be seen how frequent these ellipsoids and domes of 
undulation are in the neighbourhood of Cumbum and along the eastern 
edge of the country far to the north-east of that town. The Vinukonda 
and Nakarikallu domes are very characteristic: here the KADAPAHS have 
thinned out, and as these domes were denuded, a run of quartzites is seen 
encircling the great nucleus of cRysrALLINES. The Nakarikallu dome is 
completely insulated by gneiss; this is apparently due to faulting on 
six sides, thus giving an irregular hexagonal} outline. 
The constitution and lie of the different groups of rocks are indica- 
E TS tive of several features in the history of this 
the deposits were formed. ancient aqueous basin. Along the western shores 
are immense deposits of boulders, shingle, gravel, and sand which 
gradually become finer sandstones the further they are found from the 
* North-north-west of Cumbum. 
+ The distinction drawn between slaty or cleaved shales and slates in the present 
memoir is, that slates are such rocks as have had lamination and bedding more or less 
obliterated and in which cleavage is so strong that the rock does not split up on planes of 
lamination, as ina shale for instance, in preference to planes of slaty fracture. 
R | ۲ 19 ^) 
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