Indications of Fertility or Barrenness of Soils. 581 
The Tertiary System. 
The Tertiary System is subdivided into four portions, known 
by the name of deposits : 1, Alluvium; 2, Diluvium; 3, London- 
clay; 4, Plastic-clay. 
1. Alluvium. — Alluvial deposits are accumulations of soil which 
have been carried away by the force of water down the existing 
rivers, and which have formed, and are forming, tracts of level 
land, at the junction of those rivers with the sea, or, on their 
banks, before they arrive at the sea. 
The localities of alluvial deposits are numerous. All soils of 
this description that I have seen and examined are fertile. The 
principal of these are situated on the banks of the Esk, Derwent, 
Ouse, Trent, Humber, Thames, Avon, Wye, Monnow, Usk, 
Severn, including the Bristol Channel, on the Monmouth and 
Glamorgan coast, with numerous other localities. 
The meadows are occasionally subject to damage by sudden 
floods happening in summer, not only by sweeping off the entire 
hay-crop, but sometimes before the hay is mown, by carrying 
over the lands considerable quantities of sand and small gravel, 
which becomes entangled in, and deposited amongst the grass, 
thereby rendering it harsh and difficult to cut ; and, when mown 
and made, the hay is found to have lost its virtue, being little 
better, if so good, for fodder as straw. 
It has been said that rivers running over or through a sandy 
soil, or silicious rock, will be very likely to produce an alluvial 
deposit of a barren character. I am not acquainted with a barren 
alluvial soil. The most likely rivers to produce a soil of this 
character are the Monnow and the Wye, in some measure assisted' 
by the little whimsical Trothy. The Wye has its origin in the 
Silurian formation, well known for its barrenness, and takes its 
course through the silicious rocks of the old red sandstone. The 
entire course of the Monnow is over the same rocks ; but these 
two rivers have formed at their junction a fertile meadow of con- 
siderable extent, known by the name of " Chippenham Meadow," 
close adjoining to the town of Monmouth. And there are others 
on the banks of those rivers that are much superior in fertility to 
the adjoining lands, and which do not fall very far short in their 
produce of those meadows on the Trent, Ouse, and Humber, 
which are formed of immense masses of putrid mud. Some of 
these alluvial deposits have been the work of ages, and in conse- 
quence of the materials forming them having been washed away 
from comparatively barren districts, it may appear singular that 
out of the ruins of barren materials a fertile soil should be formed. 
It may arise from a change in the mechanical structure of both, 
and a mixture of animal and vegetable matter. In a gradual 
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