60 WYNNE : GEOLOGY OF KUTCH. [PAUT I. 



rocks become not alone important features in the geology of Kuteh, 

 bub have a connexion with that of a considerable portion of Western 

 India. The upper boundaiy presents no such decided unconformity to the 

 succeeding tertiary beds as has been recordedj with regard to the 

 junction of the same groups, at a distance to the eastward, near Surat 

 and along the foot of the Rajpipla hills, on evidence much less perfect so 

 far as rock exposures are concerned.* 



The thickness of the Kutch traps, about 2,500 feet, is perhaps less 



than one half of that which is attributed to those of 



Thickness. ,, -r-. i t i ■ i 



the Deecan, and dykes, so numerous m places there, 



are rarely seen here, although the frequent intrusions in underlying 



Jurassic rocks show abundant evidence of volcanic activity, indicating 



doubtless many of the sources whence the materials of the overlying 



traps were derived. The fact that dykes are not 



a marked feature of the formation here does not 



prove their entire absence. Similarity of the rocks might often conceal 



them, and such as might be caused by filling in of fissures from fluid flows 



above would seldom occur if rapid accumulation and slow rates of cooling 



had united to prevent fissures being formed by the contraction of the 



lower masses. Instances exist in other portions of this great Deecan • 



formation where dykes are equally rare. 



As elsewhere, no single instance of an old volcanic cone has been 

 observed within these traps, nor any such local 

 arrangement of the beds as would indicate the 

 former existence of such among them. 



On the whole, the chief difi'erence between this and other sub-aqueous 

 volcanic regions is apparently the scarcity of stra- 

 tified conchiferous beds of tufi" or ash known to be 

 the distributed material of volcanic cones. Mr. Blanford has called 



* Mem., Geol. Surv. of India, Vol. VI. 

 ( 60 ) 



