172 THICKNESS OF THE MOULD CHAP. III. 



were therefore broken into small particles, 

 and whilst being placed in a measure were 

 well shaken and pressed down. Those col- 

 lected on the Terrace amounted to 124*77 

 cubic inches ; and this amount, if spread out 

 over a square yard, would make a layer 

 0*9627 inch in thickness. Those collected on 

 the Common amounted to 197*56 cubic inches, 

 and would make a similar layer *1524 inch in 

 thickness. 



These thicknesses must, however, be cor- 

 rected, for the triturated castings, after being 

 well shaken down and pressed, did not make 

 nearly so compact a mass as vegetable mould, 

 though each separate particle was very 

 compact. Yet mould is far from being com- 

 pact, as is shown by the number of air- 

 bubbles which rise up when the surface is 

 flooded with water. It is moreover pene- 

 trated by many fine roots. To ascertain ap- 

 proximately by how much ordinary vegetable 

 mould would be increased in bulk by being 

 broken up into small particles and then dried, 

 a thin oblong block of somewhat argillaceous 

 mould (with the turf pared off) was measured 

 before being broken up, was well dried and 



