380 SPENCER : THE YOREDALE AND MILLSTONE GRIT ROCKS. 
beautiful fossils in this way for some years when I first came 
across a newspaper paragraph in which the discovery of the 
process was claimed by a popular writer on geology of that day. 
A short distance further up the valley and we come to the 
beautiful little waterfall of Lumb Bridge, which only lacks 
notoriety to be much more appreciated than it is. Here a 
useful lesson in the process of valley formation may be learnt. 
The waterfall is at the head of a narrow channel worn out of 
the Kinder Grit, and the water falls over a ledge of grit having 
under it some four or five yards of shale which is continually 
being worn awa}' by the action of the spray, so that from time to 
time the ledge of grit breaks away and thus the fall recedes. Frost, 
snow, ice, floods, and other denuding agents carry on the work 
•of valley formation still further by digging away the sides of 
the ravine and carrying away the material. 
The Kinder forms the floor upon which the Third Grits were 
laid down. It is of great thickness along and near the anticlinal, 
and is often split by beds of shale into two or three beds, but seems 
to get thinner eastwards. This floor of Kinder forms an inclined 
plane from the altitude of 1,550 feet at Elackstone Edge and Black 
Hambledon down to 350 feet in the Luddenden and Ryburn valleys. 
The Third Grits were originally laid down upon the Kinder floor 
in pretty even beds of sand and mud, and afterwards hardened into 
sandstone and shale, and, upon the upheaval of the Pennine Hills, 
were, along with the Kinder and other rocks, bent and fractured in 
various directions. Since that time they have been carved into 
hills, moorlands, and valleys by the endless process of denudation, 
so that the Kinder rock has been exposed over a large area of 
the Pennine Chain and also in the valley of the Calder and its 
tributaries as far east as the valleys of the Ryburn and Luddenden. 
During the making of the branch line from Sovverby Bridge to 
Ripponden a good opportunity was afforded to local geologists for 
examining the rocks of the Ryburn valley as far as Ripponden. 
The tunnel from Sowerby Bridge Station into the Ryburn valley 
was excavated in the shales just under bed D of the Third Grits, 
