On the Geological relations, and probable Geological age, of the several 

 systems of Rocks in Central India and Bengal, by Thomas Oldham, 

 l. l. p., f. r„ s., &c„ &c, Superintendent of the Geological Survey 

 of India, 



In the valuable reports which have been given in the preceding pages, 

 the authors have confined themselves strictly to descriptive accounts of 

 the physical relations and general structure of the several groups of rocks 

 to which their memoirs relate j in few cases adding any notice of their 

 fossil contents, or discussing the value of these, as bearing on the question 

 of their geological age. There is, in truth, much good reason why such a 

 plan should be adopted, when we consider how much has yet to be de- 

 termined regarding even the succession in time of these deposits. It is 

 scarcely necessary to insist here on the impossibility of arriving at any 

 satisfactory conclusions as to the relative age, or in other words, the 

 successive appearance of different forms of organic life, when ignorant 

 of the successive order in which the rocks containing such organic re- 

 mains were formed. And further, valuable as fossil evidence is known 

 to be, in countries intimately connected where a widely spread induction 

 has enabled careful and detailed classifications to be introduced, this evi- 

 dence loses greatly in its clearness, when it is necessary to apply the 

 results to far distant and very differently circumstanced localities. In 

 such instances, as might naturally be anticipated, minute distinctions 

 often cease to be applicable, although, at the same time, nothing may be 

 found to invalidate the wider groupings. Details of physical structure 

 must, therefore, be thoroughly made out in every new country before 

 we can admit the importance of any variations in organic remains, 

 or seek to build on apparent resemblances or analogies, or even on 

 isolated cases of identity of form, conclusions as to the relative ages 

 of the rocks containing these relics of former life. 



It must in all such reasonings never be forgotten that we do know, 

 and could know, nothing whatever as to the successive changes in the 

 forms of organic life at successive periods in time, if we had not been 



