FINAL SUMMARY REPORT. 67 " 



involved no considerable erosion between the two periods of deposi- 

 tion. Some geologists would perhaps not consider this large enough 

 to be spoken of as an unconformity, and some have gone so far as 

 to class the top gypsum or limestone band and the beds of red clay 

 underneath it as " Passage Beds " (or Middle Fars), because they 

 partake of the nature both of the gypsiferous series below and 

 the red clays and sandstones above. It is largely a matter of 

 terminology, and I see no objection to the use of either of 

 the terms " unconformity " or " passage beds," provided it is 

 made plain what is meant by the term. My interpretation of the 

 sequence of events is as follows : — The gypsum-bearing series was 

 deposited in a gulf of no great depth, which became silted up- 

 and gave place to a river, with perhaps an intermediate phase 

 of salt lagoons. To effect this change land must have appeared 

 and erosion to some extent at least have taken place. In this 

 sense, therefore, there must be unconformity everywhere, while 

 here and there erosion might be very appreciable. If it were 

 everywhere an unconformity of any size, we must presuppose a 

 widespread upheaval of a very gentle epeirogenic kind, but I am 

 more inclined to the view that corrugation of the beds commenced' 

 early in the Tertiary period ; if so the fairly persistent nature 

 of the upper portion of the gypsum-bearing series and the. constant 

 way in which it is, with few exceptions, followed by the same 

 zone of red clays (zone ' ; a " of the Kurd series), are more in 

 favour of the view that there was a minimum of erosion. The 

 few exceptions in the composition of zone " a " were all obviously 

 due entirely to local lateral variation. Before the final establishment 

 of lagoon or fluviatile conditions, there were premature occurrences 

 of sucn conditions, followed by temporary submergence beneath the- 

 gulf-waters. The last premature change of this kind occurred very 

 generally over wide areas, producing the belt of red clays just 

 below the topmost sedimentary gypsum band or fossiliferous lime- 

 stone. This belt including the topmost marine bed I take to be- 

 the " Passage Beds " referred to. It denotes a final ^oscillation, 

 between marine and lagoon or fluviatile conditions ; on my maps 

 it has been included with the gypsum-bearing series below (" Fars"). 

 I am still of opinion that localities will be found in which erosion 

 has been greater, and the unconformity visible or demonstrable p 

 it may very possibly be demonstrable in some of the areas 

 mapped when more adequate maps are available. 



