68 PASCOE: GEOLOGICAL NOTES ON MESOPOTAMIA. 



Classification. 



In view of the doubtful size of the unconformity the following 

 question arises : — " If the gypsum-bearing beds are to be assigned 

 to the Lower Fars, how can the succeeding red clays and sandstones 

 be classed as Bakhtiyari ?" As stated in Report No. 2, the " Gypsi- 

 ferous Group " of Loftus was split up by Dr. Pilgrim into a lower 

 series which he called Fars and an upper which he called Bakhtiyari 

 chiefly, I take it, because the older beds are marine and the younger 

 fluviatile, and because of a dividing unconformity. Now since the 

 gypsum-bearing strata of the area I have been surveying certainly 

 include marine beds, and the red clays and sandstones of the Kurd 

 series are certainly fluviatile or lagoon or perhaps both, and since 

 the boundary between is the only place where a widespread un- 

 conformity can possibly be allowed to exist, it seems to me very 

 probable that taxially the Kurd beds are the equivalent of Pilgrim's 

 " Bakhtiyaris," and, if the erosion of the gypsum beds along the 

 boundary be small, these beds must be correlated with the higher 

 horizons of the Fars and not with the lower. For the above reasons 

 I have avoided the term " Lower Fars " and spoken of the beds 

 simply as " Fars," until the question is cleared up by connected 

 mapping between the Mosul-Baghdad-Kirkuk area and the Persian 

 Gulf. Dr. Pilgrim concluded that the unconformity, in the Persian 

 Gulf area, even where his upper Fars was present, was of consider- 

 able size and the result of gentle undisturbed upheaval. 



Pilgrim's basal gypsum stage is described as passing up into his 

 Ostrcea virleti stage in which interbedded gypsum bands occur. 

 He says, " I am not prepared to deny that the lowest beds of the 

 Ostrcea virleti division occurring immediately above the typical 

 development of the gypsum beds are not contemporaneous with 

 portions of the Fars series further north which I have classified 

 with the basal division." There is here a distinct suggestion that 

 the basal or gypsum stage increases northwards at the expense of 

 the Ostrcea virleti stage. As I have said Pilgrim was also in favour 

 of a great unconformity between his Fars and Bakhtiyari ; so that 

 •there is more than one element of uncertainty in the correlation of 

 the Mosul-Baghdad-Kirkuk area with that of the Persian Gulf. 

 In the circumstances I would deprecate the use of the adjectives 

 lower, middle and upper being used for the present in connection 

 with the Fars of Mesopotamia, and perhaps also of the term Bakh- 

 tiyari for the later series in the same region. Geology is not a mathe- 



