CX1V PROCEEDINGS OF 1HE GEOLOGICAL SOCIETY. [May I909, 



Subsequent discoveries, made from time to time in various parts 

 of the world, have seemed to show that unconformities however 

 great and extensive are by no means universal, and that in certain 

 localities especially favoured they may he bridged by a continuous 

 series of passage-beds. At the same time, it was found that such 

 passage-beds are not, as Ramsay's explanations had led us to 

 expect, of any great thickness ; indeed, more often than not, their 

 thickness is inconsiderable. This fact was hard to reconcile with 

 the admitted course of events involved in an unconformity, indeed 

 no formal reconciliation seems at any time to have been attempted •. 

 on the other hand, a suspicion seems to have arisen, felt rather than 

 expressed, that the importance of unconformities might have been 

 exaggerated. It must have been a sub-conscious mistrust of this 

 kind that led me to suppose, when first discussing the question of 

 stratigraphical time, that unconformities might be disregarded, if 

 only we assigned to every system its maximum thickness. 



It is plain that this is not the case. With increasing knowledge 

 we are returning to Eamsay's views, and unconformities are re- 

 assuming their former importance. Let us restrict our attention 

 for a moment to the great break which occurs almost all over the 

 world at or about the close of Carboniferous times. This seemed to 

 be bridged over in India. Without referring to the Salt Range, 

 where the facts are still in dispute, 1 let us pass to the section at 

 Spiti, where the Permian succeeds the Carboniferous apparently 

 with perfect conformity, nothing but the conglomeratic character 

 of the base of the Permian remaining to remind us of the marked 

 discordance which occurs elsewhere. If, starting from Spiti, we 

 proceed towards the south-east, the Permian is found to pass in suc- 

 cession over the upturned and denuded edges of the older Palaeozoic 

 systems, one after the other, until at length it rests directly on the 

 Ordovician. 2 Nothing, therefore, could be more deceptive than the 

 so-called ' conformity' at Spiti, where the basal beds of the Permian 

 are said actually to pass down into the highest beds of the Upper 

 Carboniferous. 3 The interval of time separating the two systems 

 is probably no less at Spiti than it is elsewhere ; and yet, save for 

 the conglomerate, there is nothing to indicate it. The question will 

 naturally arise whether the continuity of an apparently unbroken 

 succession is always as real as it appears. 



1 E. Koken. ' Indiscbes Perm & die Permiscbe Eiszeit' N. Jahrbuch Fesfband 

 (1907) pp. 446-546. 



2 H. H. Hayden, : Tbe Geology of Spiti ' Mem. Geol. Surv. India, toI. xxxvi, 

 pt. i (1904) p. 52. 3 Id. ibid. p. 46. 



