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Rivers drained these upland plateaux, and poured their waters, 
with large accumulations of sand and mud, eventually upon 
the limestone, and thus the Yoredale Shale and the Millstone 
Grit of Pendle Hill were laid down. 
In a view of Pendle Hill from Downham was visible a 
portion of the ancient bed of the Carboniferous Sea. The 
finest example of Millstone Grit was at Hoghton Tower. 
In the quarry at Hoghton there was a stratum of this rock 
40 feet thick without flaw. 
On the shore and flats of the Carboniferous Sea vegetation 
began to grow. This vegetation consisted of grasses, ferns, 
and peculiar forms of trees. But the area under consideration 
began to be submerged, and the vegetation was buried beneath 
an accumulation of sand and mud. Then a halt in the sub- 
sidence took place, and another growth of vegetation began 
to spring up about the shallow waters of the sea. This in 
its turn was buried, and in the course of ages this vegetation, 
by the action of pressure, and the internal heat of the earth, 
became converted into coal. During all this deposition of 
rock matter, the sea bed was going down, until in our neigh- 
bourhood the original sea bed had been submerged about 
20,000 feet. 
Wherever they had in that locality a bed of coal, they 
might take it for granted it represented a halt in the process 
of subsidence, and when they had upon a bed of coal a layer 
of shale and sandstone, it was an indication that at that 
period the sea bottom was gradually being lowered. 
No sooner were the coal measures formed than a series of 
earth thrusts were set up which were in the main from South 
and North. The result of this was that what is now the 
Ribble Valley was lifted up above the sea, and became exposed 
to the destructive effects of rain, of heat and frost, and the 
river Ribble began to carve out a new valley. But still the 
valley was' upheaved, and still the river went on deepening 
and widening the valley. This continued to such an extent 
that the Coal Measure rocks were completely swept away 
from over the area of the Ribble Valley. The upheaval 
continued, and the Ribble began its attack upon the Millstone 
Grit. The Grit was bottomed. Then the Yoredale Shale 
was upheaved, and was in its turn cleared away, and now 
anyone may see at Clitheroe and Mytton that the river is 
engaged in removing the Mountain Limestone. 
Originally the thickness of the Coal Measure rocks in the 
Burnley area was about 8,600 feet, half of which had been 
