AND NEIGHBOURHOOD. 223 



being deposited. In former papers this deposit 

 was described, but not with sufficient detail. It 

 is well known as a brownish-coloured stiflF clay 

 containing generally about thirty-six per cent of 

 alumina, mixed with variable proportions of sand 

 and carbonate of lime. It effervesces freely when 

 treated with acids. 



A series of correct analyses of it is much 

 wanted, and the above statement of its compo- 

 sition is given only as an approximation to truth. 

 As the rocks found in the Till are the most 

 interesting portions of the deposit, considerable 

 attention has been paid by me to them, in order 

 to ascertain their natures, and their external 

 characters. For this purpose one hundred speci- 

 mens of rocks have been taken from three different 

 brick yards, and after examination the results are 

 given in the following table : — 



