3G 



HAYDEN : GEOLOGY OF NORTHERN AFGHANISTAN. 



As a rule the junction of the Upper Cretaceous limestone with all 

 underlying formations occurs on a violent unconformity (see Plate 7), 

 but at Painguzar and again in the Astar-ab valley, both of which 

 localities lie to the north of the Tirband-i-Turkistan, Mr. Griesbach 

 considered the sequence from the Red Grit series into the Upper 

 Cretaceous limestone a perfectly conformable one. 



The most complete section that I have seen lies in a small vallev to 

 the north of Ishpushta. Here, however, there appears to be an 

 unconformity, although it may not represent any particular break in 

 continuity of deposition. The uppermost beds of the Red Grit series 

 are a red limestone overlain by a red pisolitic rock very like f; low-level" 

 laterite. This is overlain by a conglomerate followed by sandstone and 

 gypsum, overlain in turn by limestone. There appears to be a slight 

 discordance at the base of the conglomerate, which, together with the 

 sandstone and gypsum, seems to belong to the overlying limestone. 

 Often, however, these beds are absent and the limestone, which is 

 usually a flaggy rock made up of comminuted fragments of shells, lies 

 unconformably on everything below. There is thus, at the base of the 

 limestone, a well-marked overlap, representing the great Cretaceous 

 transgression which affected such a wide area in Central Asia and 

 which is usually attributed to the cenomanian period (28, 290). 

 Although fossils are fairly numerous in the beds above the basal 

 limestone, I was unable to collect more than a very few and these are 

 all rather badly preserved. In Upper Saighan some shaly marls and 

 arenaceous limestones yielded echiuoids and ammonites, which mv 

 colleagues, Messrs. E. Yredenburg and G. H. Tipper, have been kind 

 enough to examine for me. I am indebted to Mr. Yredenburg for the 

 following note on the echiuoids : — 



" The four specimens of a spatangoid ecbinoderm are too crushed and too in- 

 complete for specific determination. Nevertheless the generic characters are perfectly 

 recognisable ; the specimens belong to the genus Micraster. the extremely short 

 ambulacral petals recalling forms from the Cretaceous of Europe. So far as I am 

 aware, this is the first Cretaceous Micraster obtained in Asia. None, at least, are 

 known from India or Persia. The rocks containing them cannot be older than Middle 

 Cretaceous, probably not older than cenomanian. 



