226 FORMATION AND GROWTH OF 



marl full of shells, under from 18 to 30 inches of a 

 ferriferous clayey accumulation. The former, when 

 turned up to the surface during the drainage opera- 

 tions, was found to be most productive; while the 

 latter would not grow any crops until it was well 

 limed. Some of the iron in this accumulation was 

 probably due to the decomposition of the blackish, 

 ferriferous limestone of the neighbourhood, but a 

 great deal of it evidently came down in the waters 

 of the Slaney and its tributaries from the Silurian 

 and Metamorphic rock and Granite country on the 

 west and north-west. 1 



When a surface is exposed to meteoric influences, 

 it dries and cracks ; chemical action is also at work, 

 the latter being augmented by the frequent changes 

 from wet to dry. At first the growth of soil goes 

 on very slowly, as wind or rain may carry away a 

 large portion of the disintegrated matter ; once, how- 

 ever, vegetation begins, it gets on more rapidly, the 

 atmospheric influences being enabled to work more 

 readily in depth along the holes, crevices, and the 

 like, due to the roots of the plants and the animals 



1 In general, bet ween the blue marl and the ferruginous, clayey stuff 

 there is a greater or less stratum nearly altogether composed of shells, 

 as if life had suddenly been destroyed. If this has been the case, it 

 points to a sudden partial upheaval of the land, or, as appears to me 

 more probable, a ponding up of the water by a change in the position 

 of the banks and shoals, the ponded-up water evaporating more or less 

 every low tide, and the iron from it destroying life. Or fresh water 

 may have been ponded in, which would have the same result . 



