102 THE FOSSIL ECHINOIDEA 



sometimes, but less frequently, dark grey ; the texture varies from hard, close, and 

 homogeneous, breaking with a conchoidal fracture, to soft, coarse, and open. Ordi- 

 narily, the Nummulitic limestone is tolerably compact but not crystalline, and chiefly 

 composed of Foraminifera, especially Nummulites, which are fragmentary ; corals, sea- 

 urchins, and molluscs also abound, but the two latter very frequently only weather 

 out as casts. 



" Throughout Northern Sind, except near Rohri, no beds are seen beneath the- 

 Khirthar limestone, and the rocks which crop out west of the Sind frontier from 

 beneath the main limestone-band have already been described. The remarkable range 

 of low hills surrounded by Indus alluvium, and extending for more than forty miles 

 south from Rohri, consists of Numjnulitic limestone, having a low dip to the westward ; 

 and beneath the limestone forming the eastern scarp of the hills, on the edge of the 

 alluvial plain, a considerable thickness of pale-green gypseous clays is exposed, with a 

 few bands of impure dark limestone and calcareous shale. No Foraminifera have been 

 found in these clays, -although Nummulites abound in the limestone immediately over- 

 lying ; several species of Mollusca occur, but none are characteristic; and it is far from 

 clear whether the green clays and their associates are merely thick bands intercalated 

 in the limestone, or whether they belong to a lower group. Probably these argillaceous 

 beds of the Rohri hills represent some of the marls, shales, and clays forming the 

 lower portion of the upper Khirthar group on the Gaj river. 



" The Nummulitic limestone of the Rohri hills is softer and whiter than that of 

 the Khirthar range, a difference doubtless due to the much smaller amount of distur- 

 bance that the rocks have undergone in the former instance. A somewhat similar but 

 greater difference has been shown to exist between the Nummulitic limestone of the 

 Salt Range and that of the Himalayas in the Punjab. 



" In some places west of Kotri, a band of argillaceous and ferruginous rock is 

 found close to the base of the Khirthar group. This rock weathers into laterite ; it is 

 mainly composed of brown haematite, and appears to be found over a considerable area 

 near Kotri and Jhirak. It is impossible to avoid suggesting its identity with the 

 ferruginous lateritic bed found in a similar position in Guzerat, Cutch, the Salt Range, 

 and the Sub-Himalayan region. 



" In the Laki range the Nummulitic limestone rests unconformably on the Ranikot 

 group. The Khirthar group here cannot be more than 500 or 600 feet thick, and 

 consists entirely of limestone. To the south-east, towards Kotri and Tatta, there is no 

 unconformity between the Ranikot and Khirthar groups, but, on the contraiy, there is 

 an almost complete passage between the two, and the limestone of the latter becomes 

 much split up and intercalated with shales and sandy beds. This is even more the 

 case further to the south-east in Cutch, where the whole group consists of comparatively 

 thin beds of limestone, interstratified with shales. To the south-west, near the Habb 

 river, the massive limestone dies out altogether ; and although it is well developed in 

 the southernmost extremity of the Khirthar range, near Karchat, about 50 miles south 

 of Sehwan, it disappears within a distance of 25 miles, and in the ranges on the Habb 

 river is entirely replaced by shaly limestone, shales, and thin beds of sandstone. Some 



