52 TALCHEER COAT. FIELD. 



the whole lower series, which may most justly be viewed as one great 



bed, which, as a general rule, is shaly above and sandy beneath, although 



in the shaly portions interstratifications of sandstone are not infrequent, 



while in the sandstones beds are found so fine as to resemble tripoli. In 



Traces of organic re- t^iese occur the organic remains observed in this 



'^™'^" group, and they consist only of fragments of 



stems, too imperfect to allow their affinities to be determined. On the 



rippled surface of a thin bed of sandstone alternating with shale 



near the village of Purongo, annelide tracks have 

 Aimelide tracts. 



been discovered. (PI. 1. Fig. 1.) 



The coarser sandstones frequently contain, in considerable quantity, 

 small irregular fragments of a blue shale precisely similar to that which 

 is interbedded with them ; and as there are no indications of any older 

 sedimentary rock in the district from which these fragments could have 

 been derived, while their angiilarity precludes the idea of their having 

 been derived from any distant source, there appears at first sight a 

 difficulty in accounting for their appearance, which may perhaps be due 

 to the following cause. 



It may frequently be observed in the larger rivers of this country, 

 as the Brahmini and Mahanuddi, (which during the rains bring down 

 large quantities of water with considerable velocity, so that coarse 

 sand is the only detrital matter deposited in their beds), that when 

 during the dry season they retire into a much diminished channel, 

 large pools of water charged with fine sediment are isolated in the 

 depressions of the bed of the river. These being at rest, gradually 

 deposit this fine sediment in the form of a superficial layer of mud, 

 which, on the evaporation of the water, becomes hardened by the sun 

 into a kind of shale, in many instances almost undistinguishable from 

 that of the coal measures above described. 



This, moreover, frequently cracks and breaks up into small irregular 

 fragments, which, upon a sudden influx of water, (e. g. on the occurrence 



