682 Chronicles of Science. [ Oct., 
formations over considerable areas. Of the most important coal-fields, 
those already completed are the following :—North and South Wales, 
Bristol and Somersetshire, Forest of Dean, Forest of Wyre, Coalbrook 
Dale, North and South Staffordshire, South Lancashire (on the 1-inch 
and 6-inch scales), Warwickshire, Leicestershire, Derbyshire, and part 
of Yorkshire. In Scotland the coal-fields of the Lothians and Fifeshire 
have been published on the two scales above mentioned; and in 
Treland several of the coal tracts, economically of small importance, 
have also been examined. 
The importance of completing the survey of the country surround- 
ing the metropolis has for the last few years been steadily kept m 
view, so that the “London basin” has been completely enclosed, 
together with the rich district of the Weald of Kent to the south of it. 
As the Chalk and Greensand formations may be regarded as reservoirs 
of water, which are even now very largely drawn upon by the Artesian 
wells of the city, the accurate delineation of the extent of these water- 
bearing formations possesses more than a mere scientific interest. 
Having completed that part of England which may be described 
as lying to the west of the line of the Great Northern Railway, and 
south of the valley of the Thames, the course of the survey would, 
under ordinary circumstances, have extended into the purest agricul- 
tural district of the Eastern counties. Here the geological maps 
could have possessed little or no economic value. ‘This being so, it 
has been represented very forcibly to the director-general (as we learn 
from the report for 1863) that there would be greater practical utility 
in employing the staff of surveyors on the remaining Northern counties, 
so rich in their stores of coal, iron, and other minerals of the Palzo- 
zoic age, while the Eastern counties, formed of drift-covered strata of 
the Secondary and Tertiary periods, might be allowed to wait till after 
the completion of the former. Sir Roderick Murchison states that he 
has recognized the force of these representations, so that we may expect 
the six Northern counties, with their important coal-fields, will in the 
course of a few years be geologically portrayed on the Ordnance maps. 
An important branch of the Geological Survey is the preparation 
of vertical and horizontal sections; the former for the purpose of 
showing in columns, on a scale of 40 feet to an inch, the vertical 
succession of the strata; the latter to illustrate the geological structure 
of a particular line of country, down to a natural scale of 6 inches to 
a mile, and with a datum of the sea-level, or a thousand feet below. The 
horizontal sections are all actually levelled, and represent in outline 
the natural features of the country ; not the distorted undulations of 
a railway section. In these sections the outcrops of the coal-seams, 
the boundaries of the formations, and the faults are shown in their 
true places as far as can be determined, and thus we obtain a repre- 
sentation of the interior of the earth as it would appear if laid open 
along this line down to the level of the sea, or lower. In Wales and 
other districts, the sections have been carried across the highest 
mountains, and give a faithful outline of the surface along definite 
tracts of country or across precipitous descents, where the most acdven- 
turous climber seldom dares to tread. 
