FUR EA LES. 2H 
NEW PUBLICATIONS. 365 
mechanical constitution. The ridge of chalk-down that forms the rim 
that encloses the tertiary strata of the Lanne Tunis stretehing from 
Hampshire and Wiltshire, through Berksl ishire to Cam- 
bridgeshire, and the north-west of Essex, only just touches the extreme 
. limit of Middlesex at two points. On the south of this, filling up rather 
more than the northern half of the county,—reaching down on the east, 
within the metropolitan limits, to Regent's Park and Holloway,—the 
London clay fills up the whole of the low levels, capped only with the 
barren sandy and gravelly beds of the Middle Eocene in a few places 
on the ridges, as at Harrow and Hampstead Heath. The greater part 
of this elay tract is covered with soil that is far too tenacious to be fit 
for arable cultivation. **In few counties," writes Mr. Clutterbuck 
(see p. xxv.), “is the meadow and arable land so nearly divided, or the 
extent so clearly defined; and though not without exceptions, the sur- 
face occupied by the London clay and the valley-drifts respectively, 
determines the extent under grass and under the plough. The part of 
the county in which the London clay is at or near the surface consists 
of gently rising hills, with small valleys gradually worn away by the 
surface drainage. In the farms, all operations are made subservient 
to haymaking for the London market." In the southern tract, which 
fills up rather less than half of the county, the surface beds are valley- 
drift (gravel, brick earth, and alluvium), and the soil is much more 
tractable and fertile. The eastern part of this tract is now nearly all 
built over. Passing westward to Chiswick, Hammersmith, Isleworth, 
aud Brentford, what is not taken up by houses, roads, and parks, is 
almost all occupied by market gardens; and this leaves only on the 
west a tract of about ten miles across each way between Twickenham 
Staines, and Uxbridge, in which corn is grown to any cuntidenble 
extent. Our authors’ sketch of the physical geography and climate of 
the county is very full and clear. The only point on which we have 
any fault to find is, that they have not understood clearly the rela- 
tionship of the British to the European flora as influenced by climate. 
As this is an important point, and their misconception will very likely 
lead others astray, we will quote their paragraph on this subject, and 
interpolate a running criticism on the sentences. 
* Plants which would not bear complete exposure to frost will iin 
survive, with slight shelter, frosts of short duration; and near the 
western coasts, where the influence of the sea has greater effect, espe- 
