20^ 
Jiecords of tlm Oeolojkal Survey of India. 
[vOL. XIII. 
Geological features ,—Tbe rocks forming tlio Arvali range belong to tlio 
gneissic or metamorpbic series and tbe lower transition or sub-metamorphio 
series. Tire latter series consists of schists, slates, limestones, and quartzites, and 
Las been called the Arvali series. All the sections across the range show that 
the rocks have been gi'catly disturbed, folded, and repeated several times. Tho 
flip is always high, seldom less than 70°, and often vertical. The most prominent 
features in the range are formed by tho quartzites, the highest member of the 
Arvali series; thus, Taragarh hill near Ajmere, 2,855 feet above sea level, is 
formed of this quartzite, as well a.s the ridges immediately we.st of the Sambhar 
lake, one of which rises to tho height of 2,430 feet, and tho ridges of quartzite, 
of the southcTO poi-tion of the range, south of Todgarh, attain an elevation of 
upwnrds of 4,000 feet above the sea. 
Complete sections of the Arvali series, from the gneiss to the top quartzites, 
arc exposed both to tho south, near Ajmere, and to the north of the Sambhar 
lake in Shaikhawati, but in the neighbourhood of the lake only a skeleton of the 
range is left, consisting almo.st entirely of vertical ridges of quartzite, the lower 
and softer slates, schists, &c., having for the most part been worn down below 
the level of tho jilain and covered bj^ the alluvium and blown sand. 
Several outcrops of tho Arvali schists occur on tho shores of the Sambhar 
lake, particularly a few mile.s W'est of Sambhar. The only other rocks exposed 
arc portions of two broken, roughly parallel ridges of quartzite, one at tho 
western end of the lake, and the other near the centre, a short distance east of 
Nanw’a. The famous marble quarries of Makrana are situated on the western 
side of tho range, about lO miles due west of the lake. 
No rocks are exposed in the bed of the Didwana lake, but a considerable 
thickness of slates occurs in tho hills a .short distance to the w^est; there are also 
some hills of quartzite at Kolia and Patan, a few miles distant from the lake. 
Besides the motamorphic and sub-metamoi'phic rocks of which the central 
range is composed, another scries of rocks, tho Vindhyans, occur near it on the 
w'estei’n side. The eastern boundary of these Vindhyans runs from Sojat to Kh;ltu, 
at a distance of about 20 miles fr’om the western edge of the range. West from 
this line they extend almost continuously to the west of Jodhpore. Tho 
Vindhyans of this area consist of sandstone, limestone, and conglomerate ; they 
are but slightly disturbed, being mostly horizontal, and seldom dip at a higher 
angle than 5°. They rest quite unconformably upon the Arvali series. Good 
sections of this unconformity ai’e exposed both at Sojat and Khatu, where the 
nearly horizontal sand.stone of tho Vindhyans rests upon the edges of the vertical 
Arvali slates. 
As no fossils have as yet been found cither in tho Vindhyan or Arvali series, 
their age cannot be determined with any- certainty. There is a great break 
between the Vindhyans and the Gondwanas, the next series in ascending order; 
and as the lowest group, the Talchirs, of the latter are probably permian, the 
Vindhyans are not likely to be younger than the carboniferous and possibly much 
older. The unconformity between the Vindhyans and the Arvalis is very great, 
it is almost necessary to suppose that the Arvali range was formed previous to 
