10 
Records of the Geological Survey of India. 
[VOL X. 
Geological Notes on the Great Indian Deseet between Sind and Rajputana. 
By W. T. Blanfoed, A.B.S.M., F.R.S., &e., Geological Survey of India. 
I. - Introduction. 
The following notes were made during two traverses of the great desert region east 
of the Indus,—the first from Sehwan on the Indus through Umarkot, in the Thar and 
Parkar division of Sind, to Jodhpur, vid Bahmr, the second further north and in the 
reverse direction, from Jodhpur to Rohri on the Indus, via Jesalmir. The length of the 
first traverse was above 350 miles; of the second about 300. 
The only previous geological notices of any part of this tract with which I am 
acquainted consist of a few remarks by Dr. Carter in his “ Summary of the Geology of India 
between the Ganges, the Indus, and Cape Comorin,”* * * § principally relating to the occurrence 
of granitic rocks near Balmi'r, and of some further details procured by the same author 
from Dr. Impeyf concerning the rocks seen on a journey from Rohri to Jodhpur vid 
Jesalmir, Dr. Impey’s most important observations being the occurrence of ammonites at 
Kuchri and of fossil wood at Lathi. The ammonites were referred by Dr. Carter to 
A. opis, Sow., a Jurassic species found in Cutch (Kachh). 
The physical geography of the region has been frequently described; the latest and 
best description with which I am acquainted being by Sir H. B. E. .FrereJ. On this subject 
l have already published some notes recently§. 
II.— Desceiption of Route from Umabkot to Jodhpue. 
Sandhills and lakes east of the Eastern Narra .—From the Indus near Sehwan to 
the Eastern Narra, the route lay over the alluvium of the Indus Yalley. The Eastern 
Narra is an ancient river channel by which the Indus probably, at one time, poured its 
waters into tbe western portion of the Ran of Cutch. Immediately to the east of the 
Narra a change takps place, nearly the whole surface of the country being composed of 
sandhills running in parallel lines with a general north-east—south-west direction. Between 
tbe sandhills are long stretches of water, many of them extending for as much as 15 or 20 
miles, of considerable depth, supplied from the Narra. Farther to the eastward, amongst 
the sandhills, are isolated pools of water, all of them salt; the saltest, which are a saturated 
solution of brine, being furthest east and containiug, besides common salt, sulphate of lime 
in sufficient quantity for crystals of gypsum to be formed. These salt-ponds are at a lower 
level than the long lakes near the Narra, and apparently derive their water from the latter 
by percolation, for water always runs in at their western extremities, and the salt must be 
derived from the soil. It is evident that the original surface of the country can have been 
no higher than the bottom of the lakes, which is at a depth of many feet below the channel 
of the Narra, itself beneath the general level of the Indus alluvium. It is also manifest 
that the soil beneath the sandhills is strongly impregnated with salt. Both these circum¬ 
stances are in favour of this tract of country having been an arm of the sea in recent 
times, and this probability is confirmed by the existence in some of the brackish water lakes 
of a mollusk, Potamides ( Pirenella ) Layardi, II. Ad., which inhabits salt-lagoons on the 
coast, and must in all probability have found its way to these now isolated pools of water 
when they were in communication with the sea. 
* Jour., Bombay Br. R. A. S., Vol, V, and Geological Papers on Western India, p. 633. 
+ Jour., Bombay Br. R. A. S., Vol. VI, p. 161. 
t Jour., Roy., Geog. Soc., 1870, Vol. XL, p. 181. 
§ Jour. A. S. B., 1876, XLV, Pt. 2, p. 86. 
