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been rolled, and not merely rubbed on one side. Ordinary 
wave-action on a sea beach would appear to have been a 
principal cause of their attrition. Comparatively few of them 
are uniformly striated. The scratches run all round the 
stones, and the small grooves cross each other at all angles. 
The striations, along with the polished surfaces exhibited by 
these stones, can be easily explained by the irregular and 
repeated action of coast ice. To coast-ice laden with boulders, 
stones, and debris, and floating on the surface of oceanic 
currents, we may likewise attribute the distribution of the 
coarser part of the deposit, which presents the appearance of 
having been dropped down on a sea bottom.* Above and 
around the more stony accumulations, we often find a con- 
siderable thickness of rudely- stratified clay with few or no 
stones, which may have been assorted by the ordinary 
action of the sea.f The blue-clay deposit is frequently made 
up of limestone and shale graduating from shale boulders 
down to fine clay. The greater part of it is evidently crushed 
or washed shale and broken limestone. At least seven-eighths 
of it would appear to have been manufactured out of what 
may be called the raw shale and limestone of the plain of 
Craven and ramifying valleys. It must have been principally 
derived from the lower Yoredale and upper limestone shales. 
The boulders would appear to have come chiefly from the low- 
lying limestones of the Craven district. I have principally 
examined the greyish-blue clay deposit in the valleys, valley - 
expansions, and plains between Leeds and Settle. Patches 
* Not all at once, but in a successive manner, by different masses of floating 
ice, so as to prevent any general stratification resulting from the specific gravity 
of the materials. 
f The facts presented by drift-phenomena, and not any prevailing theory, 
must approximately determine the degree of cold during any stage in the sub- 
mergence or emergence of the land, and the nature of the accompanying glacial 
conditions, whether arising from astronomical or geographical causes, both acting 
in concert, or the one neutralizing the other. 
