Correspondence. 347 



the blocks ; the icefloes serving as rafts, would suffice to convey the 

 blocks to other parts of the coast, whilst they would not require any 

 great depth of water to float them. 



Discussion. — Mr. Hughes pointed out some difficulties in accepting the theory of 

 the transport of these hlocks by means of coast-ice, but was not able to offer any 

 better solution of the question than that suggested by the author. 



ooiaiEaESiPOisruEn^OE. 



THE BOULDER-CLAY OF CAITHNESS. 



SiK, — In the first part of his paper on this subject, Mr. Croll says, 

 " The notion that unstratified Boulder-clay could be formed by de- 

 posits from floating ice is not only erroneous but is also positively 

 pernicious." 



The great chalky boulder-clay or uppermost of the glacial deposits 

 of East Anglia, though of great thickness, is everywhere destitute 

 of stratification, and, according to Mr. Croll's dictum, no part of it 

 can have been deposited from floating ice. This clay, however, rests 

 over large districts upon a thick sand and gravel formation : and it 

 may be seen in coast sections some miles in length thus to rest con- 

 tinuously, the sands below it being finely stratified and of undis- 

 puted marine origin. The junction of this unstratified clay with 

 the sands is there quite undisturbed, presenting an even line of 

 transition ; while in other sections a passage-bed, a few feet in 

 thickness, formed of the sand and clay interstratified, not unfre- 

 quently marks the junction. 



Now, had a mass of ice pushed over this sandy sea bottom, and so 

 produced the unstratified boulder-clay thus covering it, or had that 

 clay itself been pushed over the sands, these could not have escaped 

 being squeezed up and contorted, instead of having, as is the case, 

 their stratification undisturbed up to the very line of junction. 

 Instances, moreover, occur where this unstratified clay makes a dip 

 into the previous sandy sea-bottom ; and where a cross section of 

 such a dip can be obtained, the sands are found undisturbed, ex- 

 cept in the space ploughed, a feature obviously pointing to the 

 impact of a floating body upon the sea-bottom. In rare instances, 

 threads of sand a few inches thick occur in this unstratified clay ; 

 and if there chance to be two such threads together, their horizon- 

 tality to each other is preserved. Conversely to this, I may add, 

 that a band of this unstratified clay, two or three feet thick, but in 

 all respects undistinguishable from the mass of the boulder-clay 

 itself, is to be found in some instances interbedded in the sands 

 and gravels to which I have just alluded, the stratification of these, 

 both above and below such band, being quite undisturbed. 



I dissent from so many of Mr. Croll's views that I would not 

 have troubled you with this letter upon only one of them, but that I 

 am unwilling so unqualified and denunciatory a statement should 

 remain longer without a traverse. 

 Brentwood, Essex. Sbaelks V. WoOD, JuN. 



