During the last few years the rocks in this area have been mapped in considerable detail by the Geological Survey, and the results which are coming out seem likely to throw much light upon the physiography of Carboniferous seas and perhaps upon the genesis of some limestones of other ages. It was always a puzzle to those geologists who knew the ground how it came to pass that the well-known and very persistent series of the several limestones of the Yoredale Beds ran with such regularity over the great area of the Yorkshire dales and yet were not recognizable over the area of Bowland and the southern part of Craven. Until the area of which we now speak was carefully surveyed, it was assumed that there was a rapid transition of type in the Carboniferous Rocks between Clitheroe and the big fells north of Settle and Malham, but as to the cause of such a rapid change no explanation was forthcoming. Even Professor Phillips, who knew the country perhaps best of any among the old pioneers of Geology, often expressed himself to me as quite unable to account for it. If there is one thing more clearly brought out than another by the mapping in detail of this ground, it is this, that there is absolutely no transition from one type to the other. The two types run unchanged in their respective areas and with complete discordance with each other, quite up to a common boundary where the differences are ...