THE PATLI DUN. 57 



pelago, described the great influence exerted by the sharp though 

 marked geographical line of division (Wallace's line) between those 

 islands of the Archipelago which belong to the ancient Asiatic conti- 

 nent and those which belong to the Australian continent, in keeping 

 distinct the fauna (especially birds and mammals) of these two great 

 zoological divisions of the earth in later geological and Recent 

 times. 



We have here among the upper members of the Sub-Himalayan 

 formations a converse order of phenomena ; the unbroken sequence of 

 deposits, that is, the merging of past geological into Recent deposits 

 has carried with it a coherent chain of like forms, so that the same 

 type of animals exist now in this part of the earth (though greatly 

 reduced in the numbers of their genera and species) as existed in 

 the remoter ages of the Siwalik period. 



The present section of the Sub-Himalayan region is wider than 

 any we shall have to consider in this work. To the north of the dun 

 proper, there is a Nahan sandstone zone, a continuation without 

 break of the Nahan beds to the north of the last described section. 

 The slopes of the conglomerate south of the dun are similarly merely 

 a continuation of those which form the range to the south of the 

 Sanguri s6t ; and so is the sand-rock zone south of it a continuation 

 of the sand-rock zone described above. But the plainward edge of 

 the hills shows a change in this locality. The sand-rock hardens by 

 insensible degrees, and takes upon itself features which ultimately 

 blend with those of the Nahan sandstone : in other words, we have the 

 sand-rock passing down into the Nahans ; so that the latter now abut 

 against the plains. In the petrology of the sand-rock and Nahan 

 stages I have already indicated this passage, but without proof. The 

 present and other sections show unmistakeably that such a passage 

 does really exist. The likelihood of this was foreshadowed by Cautley 

 (Fauna Sivalensis) on fossil evidence, collected further north-west in 

 the beds near the town of Nahan, and has been discussed by Mr. 

 Medlicott (Mem. Ill, G.S.I., pp. 105, 106). Later on Ishallgoa little 

 more fully into the subject of the consequences which follow on a 



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