ist” 
than fifteen hundred. Equal attention has been paid to hydro- 
graphy. ‘The course of rivers and brooks has been drawn neither 
fancifully nor negligently, and in the new parts will be found mi- 
nutely correct. The names of the smallest streams have been also 
diligently sought and recorded; and those of rivers are generally 
inserted both at their mouths and at their forkings. 
In the table of formations the following changes have been made. 
The upper and lower members of the green-sand, formerly united, 
are separated by a streak of gault. The fuller’s earth, the upper 
lias marl, and the marlstone are separated from the other members 
of the Cotswold series. The new red sandstone group has been 
dissected after the manner of the Germans; and in Siluria the 
divisions first established by Mr. Murchison have broken up the 
unity of the greywacke formation. 
In determining the boundaries of the strata, Mr. Greenough has 
added to his own personal experience that of other competent ob- 
servers ; and he acknowledges among the most valuable communi- 
cations, those of Mr. De la Beche, Mr. Jukes, Mr. Logan, Mr. Mac- 
Lauchlan, Mr. Milne, Mr. Murchison, Prof. Sedgwick, Mr. Sop- 
with, Mr. Strickland, Mr. J. Taylor, Mr. N. Wood, Mr. Lonsdale, 
Dr. Fitton and Mr. J. Phillips. 
On comparing the geological boundaries of the old map with those 
of the new, Mr. Greenough hopes to be excused for indulging some 
slight feeling of self-congratulation. ‘Though almost every part of 
the kingdom has undergone within the last twenty years a rigid 
scrutiny owing to increased facilities of investigation, yet the geo- 
logical errors of the first edition are far less grave and numerous than 
might reasonably have been apprehended. The only errors which 
he thinks require to be specified, are a false colouring in Leicester- 
shire of small extent, arising from accidental carelessness, and that 
in Devonshire and Cornwall due to imperfect information *. 
The lower deposits of these counties, as formerly represented, 
consist either of clay-slate with cross courses of elvan, or greywacke 
slate, with its usual suite of greywacke, transition limestone and 
culm. In place of these is now presented Old Red Sandstone, with 
subordinate bands of limestone, mountain limestone and coal. 
This change, Mr. Greenough says, will no doubt appear uncalled 
* Mr. Greenough states in a note, that between the representation of the 
Cornish and Devonian rocks, and that put forth in a small skeleton map by 
Professor Sedgwick and Mr. Murchison, the resemblance is so obvious, that 
it is necessary for him to notice only the difference. The object of their 
map, he says, was to disconnect the Devonian from the older transition beds, 
in his to connect them. Hence the colour chosen by them presents a con- 
trast to that of. the Cambrian, which he proposes to term the lower killas 
system; while that which he has chosen presents an attempt, however im- 
perfect, at approximation. ; 
The Devonian rocks, Mr. Greenough has always believed, and still be- 
lieves to agree with those of the Hartz; and if Professor Sedgwick and Mr. 
Murchison arrive at the same conclusion, they will only confirm, by the high 
authority of their names, the correctness of a doctrine laid down in the 
former edition of the map, as well as the present. 
