492 TIDDEMAN : CARBONIFEROUS ROCKS IN UPPER AIRE-DALE. 
or Bowland series for tlie Yoredale type, and if we could realise the 
state of affairs when these rocks were forming, we shoukl probably 
say that we had left a deep sea dotted witli islands and come on to a 
wide and long and shallow reef. 
The long history of that reef and its denizens from its early 
foundation on a slowly sinking plateau of slate rocks, to its last 
phase wdien the animals which lived on it, and formed it, had to 
succumb to conditions fatal to their existence, the recurrence oft- 
repeated of favouring or fatal environments, the movements of 
submergance and emergence connected therewith, the set of tides 
and currents, the transport of material, these and many other matters 
may be read in the Mountain Limestone and Yoredale Series, but as 
yet they are written only in the rocks. 
