J. K. Creighton — On " Pigotite'^ in Cornwall. 223 



Some years ago I described before the Glacialists' Association 

 beds of gravel containing rolled clay balls, occurring at Offerton and 

 Eomiley in Cheshire. These beds form the cores of glacial mounds 

 which can be exactly matched by mounds now being formed by 

 glaciers in places the sea does not reach. 



The most ardent supporters of the submergence hypothesis would, 

 I think, hesitate before attributing such mounds to shore action, 

 even though they contain clay balls. 



Is the pi-esence of clay balls in a deposit proof of shore conditions 

 in a tidal sea ? Running water may be essential to their formation, 

 but surely there would be enough of that in the drainage system 

 of a great glacier. 



But we are told " if they were constantly immersed they would 

 get dissolved." Why have they not been "dissolved" out in their 

 present situation ? The conditions could hardly have been more 

 favourable, for the gravel lies between two impervious beds of 

 boulder clay and forms a natural line of drainage. 



The reason is best given in Mr. Reade's own words. The " balls 

 are covered over their surface with small gravel, shells and sand." 

 They are thus armour-plated, and Sir Henry de la Beche^ pointed 

 out the significance of this fact long ago. He shows that clay 

 containing fine gravel would not be acted on by running water 

 with a velocity of less than 12 inches per second. 



It is then no question of getting " partially dried during recession 

 of the water twice in 24 hours," and their presence in a bed affords 

 no evidence of tidal action. 



Glacialists will thank Mr. Reade for responding to their request 

 to show them the shore lines of the supposed glacial sea, but to 

 be convincing they must be supported by evidence different from 

 that given in his paper. 



Postscript. — Since the above was written an article has appeared in 

 the Glacialists' Magazine (March, 1894) by Prof. N. H. Winchell, 

 State Geologist, Minneapolis, Minn,, on " Pebbles of Clay in 

 Stratified Gravel and Sand." 



He gives several instances" of clay balls occurring in stratified 

 drift in America, and in places where marine action was quite out of 

 the question. 



He concludes that clay balls " may be produced and embedded in 

 gravel and sand which was the direct result of the wastage of the 

 glacier, and that they are not unquestionable evidence of the former 

 action of an oceanic shore line." 



Till. — On the Occukrence of Pigotite in the Caves near 



PORTHCURNOW, St. LeVAN, CORNWALL. 

 By J. K. Creighton. 



HAVING heard from my esteemed friend and colleague, Mr. 

 J. W. Wetherell, that some years ago a brown crystalline 

 substance had been found in a cave close to the sea, and situate 

 1 Geological Manual, p. 51. 



