12 GEOLOGY OF THE SON VALLEY, ETC. 



Western and Central Provinces", and repeated in the two editions 

 of the Manual of the Geology of India. Mr. Mallet's zones are as 

 follows x : — 



ii. Limestone. 

 10. Shales. 



9. Limestone. 



8. Shales, sandstone, 



7. Limestone. 



6. Shaly sandstone. 



5. Porcellanic shales. 



4. Trappoid beds. 



3. Porcellanic shales. 



2. Limestone. 



1. Conglomeritic and calcareous sand- 

 stone. 



This classification was formed in the eastern part of the Son 

 valley exposure of lower Vindhyans, beyond 



Subdivision into stages. . 



the limit of the map attached to this memoir, 

 and in that area all the eleven zones can be readily recognized. 

 In the western area it was found that though the sequence on 

 the whole resembled that described by Mr. Mallet, the individual 

 zones could not be recognized with certainty and a more general- 

 ized classification was adopted as follows :^ 



4. Rohtas stage. 

 3. Kheinjua stage. 

 2. Porcellanite stage. 

 1. Basal stage. 



Of these the lowest includes Mr. Mallet's Nos. 1 and 2, the Porcel- 

 lanite stage his 3, 4, and 5, the Kheinjua stage, his Nos. 6, 7, and 8, 

 and the Rohtas stage Nos. 9, 10, and 11. 



It must, however, be borne in mind that these stages are not 

 separated from each other by well-defined horizons. They merely 

 represent different facies of deposits which pass into each other, 

 1 Mem., Geol. Surv. Ind., Vol. VII., p. 28. 

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