94 THE POIKILITIC PERIOD. CHAP. 



The preceding observations apply to the filling up of a submarine 

 area, or sea-bed, and to a given period of time. If we conceive 

 the process to go on, so that at last the whole basin may be filled, 

 or nearly so, and filled under the influence of storms and calms 

 and tidal ebb and flow, the results may be modified. The water 

 forces being greater at intervals, will then distribute the gravels 

 and sands to greater distances from the shore : the several kinds 

 of matter may be somewhat mixed, and there may be alternations 

 of them. There may be sandy conglomerates, and argillaceous 

 sands ; and there may be alternations of these, especially in the 

 upper parts, where, by reason of the shallowing of the water, the 

 force of the waves and currents becomes sensible on the sea-bed 

 far off from the land. Thus gravels and sands are accumulated 

 in patches, and form banks, and clay settles in the least disturbed 

 and relatively deepest parts of the sea. The clay beds always re- 

 tain the character of greater continuity and more uniform thickness, 

 and greater distance from shore. 



In a continuous system of sedimentary deposits there may be 

 zones of mineral distinction among the sediments not parallel to 

 the horizon, interspersed patches of coarser ingredients, and con- 

 nected sheets of argillaceous ingredients. These latter are often 

 the best marks of contemporaneity. 



The Poikilitic series appears all round the liassic border of the 

 Thames basin, but never enters it. An interesting development 

 is known in the district of Coventry and Warwick, where, with 

 some difficulty and not without hesitation, the three elements of 

 Permian, Bunter, and Keiiper have been recognized, the two first 

 being very near of kin. The series stands thus, much as at 

 Malvern : 



Red marls. 



Upper (Keiiper) sandstone and marls. 



Lower red marls. 



Lower (Bunter) sandstone. 



Permian beds. 



This series is fossiliferous ; reptilian remains and shells being 

 not indeed plentiful, but yet found at several places, from whence 

 they have been collected by Dr. Lloyd, the Rev. P. B. Brodie, 

 and other geologists, and placed in the Warwick Museum. 



