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5.— GEOLOGICAL CONSIDERATIONS. 
T’he conspicuous success (Chart VII.) of the crab in the 
northern division of the County, I am persuaded is closely con- 
nected with the geological conditions. At all the stations, the men 
know that the crabs from a hard bottom are, as a rule, of better 
quality than those from a soft bottom. Now it is a fact that the 
crabs in the northern district are not only much more numerous, 
but taken as a whole of better quality than those of the 
southern, and it is a fact likewise that the hard gromid is much 
more extensive and extends further to sea in the former region. 
The great areas of hard ground permit of more extensive move- 
ments on the part of the crabs in the northern half of the County. 
Their migrations are wider, greater dispersion occurs, and this 
means there is a larger extent of feeding ground at their disposal. 
The soft ground is much nearer the coast in the southern 
district, and limits migration and the available feeding space. It 
follows that the depositions of mud from the Tyne at the southern 
limit of this latter district will tend to further contract the hard 
ground. 
The crabs appear, moreover, to differ to some extent in size in 
different localities, and in some places a segregration of sex is said to 
characterize various grounds. 
On the other hand, the more littoral rocky ground of the south- 
ern half of the County is about equally favourable to lobsters as the 
northern, and the fact offers a physical proof of the conclusions with 
regard to the migration of this form which we have arrived at from 
experiment. 
To illustrate this point, I made enquiries as to the extent of the 
hard ground off the Northumberland coast, and indicated its limits 
on a map of the district, which is here reproduced (Chart XII). It is 
only approximately correct, but its value has been greatly increased 
from additions to it made by Professor Lebour, showing the probable 
trend of the formations under the sea, and with regard to this he 
has written the following note : — 
“ On the accompanying map, an attempt has been made to indicate the 
probable position of the outcrops of the various geological formations beneath 
the surface accumulations upon the sea-bottom for some miles east of the coast 
line. It is possible that some of the tracts reported by dredgers as consisting 
of “ Hard Ground” may actually be occupied by portions of these outcrops in 
situ kept bare by current action, but for the most part these areas are, there is 
reason to believe, covered rather by detached fragments of the outcrops over 
which they lie, together With other fragments carried by current action some 
