Reviews—J. V. Elsden—Agricultural Geology of Herts. 521 
“Faune du Calcaire Carbonifére de la Belgique,” especially in refer- 
ence to the spines of Oracanthus (Antacanthus, Dewalque). Many 
of the specimens of these spines in the British Museum show 
palpable evidence of wear along their distal extremity, as so well 
seen in the pectoral spines of Gyracanthus from the Coal-measures 
and in those of the living Silurus. 
It seems probable that they may have occupied a lateral position 
on the head of these old Elasmobranch Fishes. That these spines 
of Oracanthus were not true dermal plates is proved by their apices 
being solid, and decorated on both sides. That they were lateral and 
not dorsal defences is proved beyond doubt by the worn condition of 
their apices; but there is no reason to justify the idea (p. 530) “ that 
they formed the posterior termination of the body.” 
Space does not permit us to enter upon a detailed discussion of the 
numerous genera and species which Mr. Davis brings before us in 
his Monograph. Ata future time we may venture again to refer to 
his work. Suffice it to say, that for one who has to accomplish his 
task as Mr. Davis does, in the hours of leisure (often few and far 
between) which a busy manufacturer can spare from his daily 
avocations, and with the drawback of being located at a distance . 
from the great museums and libraries, one cannot but feel that he is 
entitled to our most favourable consideration and our best thanks. 
IJ.—Tse AcricuntturaL GroLtocy or Hexrtrrorpsaire. By J. 
Vincent Espen, B.Sc., F.G.S. From the “Transactions of 
the Hertfordshire Natural History Society,” vol. ii. part 4, 1883. 
ETER some remarks on the relation of Agriculture to Geology, 
and especially on the differences in cultivatible Jands in dif- 
ferent parts of England and Wales as being due to geological struc- 
ture, and to relative rainfall on the high and low grounds, Mr. Elsden 
proceeds to describe the climate and physical features of Hertford- 
shire in particular. The annual rainfall (ranging from 25-7 to 34:6 
in different parts of the County) is given in a table; and the more 
important physical properties of the soils of Herts are carefully 
tabulated, showing their relation to water and temperature; and 
all the results are found to be in accordance with the local geology. 
The range, limits, and characters of Alluvium, Boulder-clay, 
Glacial Gravels and Sands, Brick-earth, Clay-with-flints, Pebble- 
gravel, London Clay, Woolwich and Reading beds, Chalk, and 
Gault are concisely dealt with, and illustrated with a map. So also 
the local soils are described and mapped, and their probable origin 
from the several underlying or neighbouring stratified deposits 
clearly indicated. Thus (see table on page 522) :— 
The influence of the geological constitution on the agricultural 
features of Hertfordshire is further considered topographically ; the 
local water-supply being also taken into account. The reason why 
the Chalk district of Herts differs from those of the Southern Counties 
is explained by the presence of extensive argillaceous and sandy 
coatings and cappings. 
