282 Johns: The Carbontferous Rocks of the Kettlewell District. 
plateau some hundreds of feet thick, out of which the dales 
mentioned have been carved, exposing, in the case of the three 
first mentioned, the pre-Carboniferous rocks on which the 
Carboniferous series rests. There are no_ stratigraphical 
difficulties here. There is a sameness, too, about the Yoredale 
rocks that rest on this great limestone plateau, and at first 
sight this series of limestones, sandstones, and shales appear 
very simple. But the simplicity is only apparent, and when 
a large area is investigated it becomes very evident that the 
Yoredales are a very changeable series, and that these changes 
possess great significance. John Phillips, whose classic de- 
scription of the Mountain Limestone district, in his ‘Geology 
of Yorkshire,’ is still the best account of our area, was fully 
aware of this, and devoted much attention to it. His most 
important conclusion was that the typical Yoredale series 
practically disappear on the western face of Great Whernside, 
and passes into the Shale Series which lies between the massive 
limestone and millstone grit of the region to the south east. 
The significance of this important change in the lithology of 
the Yoredale series cannot now be discussed, but interest lies in 
the fact that it takes place in the neighbourhood of Kettleweil. 
To return to the Great Scar limestone and its faunal sequence: 
so far as it can be made out in the area under discussion, two 
zones can be determined. Neither are complete, but are still 
clearly distinguishable. One is characterised by the presence 
of Productus giganteus and the other by its absence. The first is 
the Dibunophyllum zone—the highest in the Lower Carboniferous 
rocks. The second one is the Semznula zone, the base of which 
is represented by the Carboniferous basement conglomerate of 
Ingletondale. Taking the Semznu/a zone first it will be found 
that only the upper sub-zone, or S, is well exposed, but it will 
be possible to obtain the characteristic fossils, though the beds 
of this age are not very fossiliferous compared with the rich 
collecting grounds in the D, beds of Wensleydale and other 
districts. In a small quarry on the left-hand side of the road 
from Kilnsey to Kettlewell, and near the last named place is a 
very interesting exposure of these S, beds, and Semznula ficordes, 
Chonetes papilionacea, Productus corrugato-hemisphericus, and 
Syringopora sp. can be obtained. To those interested in the zonal 
classification the most interesting piece of work will be to 
investigate in detail, starting from a known faunal horizon, a 
section affording a series of exposures to the top of the Great 
Scar limestone. They will thus be able to notice the change of 
Naturalist, 
