328 BAMBLES OF A GEOLOGIST. 



zontally, when the overlying vegetable mould has been re- 

 moved, and the whitened surface in immediate contact with 

 it pared off, a polygonal arrangement, like that assumed by 

 the cracks in the bottom of clayey pools dried up in summer 

 by the heat of the sun. Can these possibly indicate the 

 ancient rents and fissures of the boulder-clay, formed, imme- 

 diately after the upheaval of the land, in the first process of 

 drying, and remaining afterwards open enough to receive what 

 the uncracked portions of the surface excluded, the acidu- 

 lated bleaching fluid ? 



The kind of ferruginous pavement of the boulder-clay 

 known to the agriculturist as pan, which may be found ex- 

 tending in some cases its iron cover over whole districts, 

 sealing them down to barrenness, as the iron and brass sealed 

 down the stump of Nebuchadnezzar's tree, is, like the white 

 strips and blotches of the deposit, worthy the careful notice 

 of the geologist. It serves to throw some light on the origin 

 of those continuous bands of clayey or arenaceous ironstone, 

 which in the older formations in which vegetable matter 

 abounds, whether Oolitic or Carboniferous, are of such com- 

 mon occurrence. The pan is a stony stratum, scarcely less 

 indurated in some localities than sandstone of the average 

 hardness, that rests like a pavement on the surface of the 

 boulder-clay, and that generally bears atop a thin -layer of 

 sterile soil, darkened by a russet covering of stunted heath. 

 The binding cement of the pan is, as I have said, ferruginous, 

 and seems to have been derived from the vegetable covering 

 above. Of all plants, the heaths are found to contain most 

 iron. Nor is it difficult to conceive how, in comparatively 

 flat tracts of heathy moor, where the surface-water sinks to 

 the stiff subsoil, and on which one generation of plants after 

 another has been growing and decaying for many centuries, 

 the minute metallic particles, disengaged in the process of de- 

 composition, and carried down by the rains to the imperme- 



