576 Correspondence — Col.G.Greemvood. 



WHY ARE THE LAEGEST STONES FOUND AT THE EAST END 

 OF THE CHESIL BANK ? 



Sir, — At the risk of being charged with repetition, may I ask for 

 space to cry lo Triumphe ! that both your correspondents on 

 this subject in June last call in the stroke of the wave, instead 

 of requiring a "tidal current" to lift pebbles 42 feet above 

 its own level. This is a charming change in theory. Those who 

 wish practically to study the question have no need to go to Port- 

 land. They have only to observe the beach between any two groins. 

 They will there always find the largest pebbles heaped at the lee- 

 ward end. The reason is that when motion is given to pebbles, the 

 largest are always on the outside. Shake the sugar-basin : the small 

 sugar descends, the large lumps rise. The large outside pebbles 

 then are always most exposed to the upward and onward stroke of 

 the wave as it travels down the wind. As Portland runs out to sea 

 nearly at . right angles to the line of coast, it is a gigantic " natural 

 groin," As a civil engineer, Mr. Eeade must be well aware of the 

 resistless force of the impact given to the wave by the wind. The 

 largest blocks which man can handle with the most powerful 

 machinery, laid so as to avoid the force of the wave by the most 

 skilful engineers, in sea-walls, piers,' and breakwaters, how often 

 are they delivered protervis in mane Creticum portare ventis. Would 

 tbat I could persuade him to read chap. viii. of Eain and Eivers, on 

 the " Travelling of Sea Beach," where these things are discussed at 

 length, aad to believe that storms of wind are always washing out 

 pebbles into the clays, and forming '' Boulder-clay." Also, that all 

 travelled drift and boulders are simply the result of sea-shore tra- 

 velling. In fact, that the collection on Moel Tryfaen is a " raised 

 beach," and has not flowed up there on ice. 



Ebookwood Park, Alresfoed. George Greenwood, Colonel. 



BEHAVIOUR OF GLACIERS AND ICE-SHEETS. 



Sir, — In his paper " On Drift," in your last Number (p, 503), Mr. 

 Goodchild speaks of the separate and independent movement of the 

 upper and lower strata of ice in an ice-sheet as if it were an old-established 

 fact, "long since stated by Prof. Eamsay," indeed "that it was quite 

 possible that some of the higher parts may have moved in directions 

 directly opposite to the course taken by those at a lower level." Whilst 

 ready to concede the fact, that when the lower part of a stream of ice 

 becomes impeded in its downward course, the upper part of the pent-up 

 ice-stream will rise over and flow on beyond the obstruction, I fail to 

 understand the upper strata flowing in the reverse direction. Will Mr. 

 Goodchild make this clearer and refer us to Ramsay's observation ? 



J. Frost. 



