ECONOMIC GEOLOGY. 195 



Some of the post-tartiary calcareous beds also furnish good building- 

 material, and a gritty limestone of subrecent origin has been employed 

 for bridges, &c, on the railway at Jhimpir station. 



As the bulk of the Khirthar group, numerous beds in the Gaj (and 

 sometimes nearly the whole formation), several 

 bands at the base of the Nari beds, and extensive 

 deposits on the upper Ranikot beds, consist of limestone, the supply of 

 lime is abundant almost wherever rocks occur, or the detritus of the 

 lower beds is washed by streams. An abundance of limestone pebbles is 

 found in the pliocene and post-tertiary conglomerates. 



In the Gaj beds of the Khirthar range, near the top of the group, 

 gypsum of tolerable purity is abundant, and is 

 not unfrequently found in beds 3 to 4 feet thick. 

 Two such beds, one of them much purer than the other, occur in the 

 section exposed on the banks of the Gaj river, and thence to the north- 

 ward similar beds are of not unfrequent occurrence. Some gypsum is 

 found in- the Ranikot group, but the quantity is small. 



Some of the pyritous shales found in the Gaj beds are employed in a 

 , , rough manufacture of alum. Places where the 



Alum shales. 



salt had been made were seen on the Maki Nai 



north of the Gaj, and in one or two other places in the hills. Some has 



also been made at Ranikot from shales in the Ranikot group, and some 



from Nari shales, as at Bill, 12 miles north of Thana Shah Beg, in 



Kohistan. The manufacture is evidently rude, and has not been observed 



in progress by the members of the Survey. It is said by the natives 



to consist in merely burning the shales and lixiviating the burnt shale 



in water. Probably, however, the potash necessary for the production 



of alum is added, being procured from ashes of plants or some such 



source. 



In some places, as in the southern portion of the Laki range, and 



near Hyderabad, a pale greenish clay is found, 

 Fuller's earth. . 



which is dug and used for washing cloth, and 



also, it is stated, eaten by women during pregnancy, a common practice 



( 195 ) 



