A HISTORY OF CUMBERLAND 
there set in a very long period during which the principal materials laid 
down upon the sea bottom were beds of limestone, all of them more or 
less of the nature of the various calcareous oozes which are in process of 
formation in the deeper recesses of the ocean at the present day. There 
is no proof of the existence of anything at all resembling coral reefs ; 
although, as is well known, isolated groups of corals, all belonging to 
an extinct order, locally occurred in abundance. ‘The general nature of 
the fossils found in these limestones suggests the presence of equable and 
moderately warm surface currents, which are usually favourable to the 
development of animal and vegetable organisms. 
With the evidence we now possess it is not difficult to fill in a few 
details regarding the physical geography of the Cumberland area at this 
time. To begin with a feature about which a widespread misapprehen- 
sion exists: There is not a particle of evidence to show that the present 
Lake district represents an old island in the seas of the period under 
notice. There was, it is true, the easterly ridge already referred to ; 
but the subsidence of the sea bottom carried this below water at an 
early stage, and there is not a single fact that would indicate an area 
of even shallow water, let alone an island, which coincides with any 
part of the present Lake district. It will be shown presently that 
the Lake district as an upland area did not come into existence until 
Tertiary times. We have clear evidence of the delta of a great river, 
which represents the materials brought south-eastward from a land 
area somewhere to the north-west. As the land subsided the seaward 
edge of the delta receded in the direction of the continent. A study 
of the present distribution of the terrigenous deposits of this period (that 
is to say, the gravels, sands, and muds derived from the land, as dis- 
tinguished from the limestones) shows that the axis of the delta lay far 
to the east of the area under notice. As a consequence we find the 
proportional thickness of the deposits from clear and quiet water to that 
of those deposits which have been mechanically transported from the 
land steadily increasing as we advance from east to west. This is true of 
the rocks belonging to the period under notice, not only in Cumberland, 
but also in most other parts of the kingdom as well. 
To gain a clear conception of the sequence of events to which the 
Lower Carboniferous Rocks of Cumberland are due, the reader should 
endeavour to realize the effect of periodic subsidences of level alternating 
with periods when the land was stationary, or even subject to occasional 
oscillations of level. With a subsidence the clear water of the sea 
advances over an area where prior to that subsidence there stood the 
estuary lagoons and shallow seas of a delta, the waters of which were 
more or less turbid and laden with the materials wasted from the old 
land. While the land remained stationary the delta gradually pushed 
seaward and covered the deposits found in clear water with the 
sediments derived from the land. With oscillations of level, in which 
the net result of the movement is one of subsidence, alternations of 
deposits proper to clear water alternate with the clay, sand and gravel, 
24 
