242 CARTER : NOTES ON THE GEOLOGY OF MALHAM AND SETTLE. 
at Malham Cove to the height of 285 feet, and at Gordale to 300 feet. 
These scars are caused by the Mid-Craven Favdt, which has brought 
down the sandstones of the Millstone Grit against the compact 
Mountain Limestone. 
Leaving the conveyances at Malham, the party followed the route 
to Gordale, which is a magnificent illustration of a limestone gorge. 
Gordale is essentially a water-worn ravine, with a rapid stream wearing 
down the soluble limestone. The vertical sides of the narrow gorge 
below the fall suggest that an underground stream formed first of all 
a cavern, which was converted into an open ravine by the falling in 
of the roof. As examples of depositions may be noticed the laminated 
masses of travertine, where the water is subject to rapid evaporation, 
at Gordale Scar and in Janet's Cove. The stones in the limestone 
streams, it will be noticed, are encrusted with round masses, the work 
of an alga ( Rivularia calcarea ), which abstracts the carbonic acid 
for its nutriment, thus causing the carbonate of lime to be thrown 
down. The northern branch of the Craven Fault is exposed in 
Gordale Beck, and is filled by a wide vein of breccia. This fault 
brings down the solid limestone of Gordale against the Upper Silurian 
Grits of the Coniston Series. The base of the Mountain Limestone 
north of the fault, which consists of a kind of sandstone containing 
Silurian pebbles, was crossed on the way to the Tarn. 
Malham Tarn is a natural sheet of water about half a mile square, 
surrounded on three sides by peaty moor or bog, and on the north 
shut in by fine limestone scars. This district is the habitat of many 
rare plants, the search for which formed an interesting variety from 
the more strictly geological work. Malham Tarn stands 1,240 feet 
above sea-level, and covers about 160 acres. It fills a shallow hollow 
in the Silurian rocks, its greatest depth being fourteen feet, five feet 
being due to an embankment at the southern end, constructed first by 
Lord Ribblesdale, and afterwards rebuilt. Some mounds of sub-angular 
gravels lie east and south of the Tarn, which may be of glacial origin. 
The return journey was devoted to the examination of the 
Malham Dry Valley, which is probably unique in England in the 
perfection of its preservation. After running for half a mile south- 
wards, the stream from Malham Tarn sinks into the limestone by 
