President's Address. 19 
circumstances, they may have been preserved in rocks of 
shallow-water origin. It is, also, a well-known fact that in 
distinctively Graptolitiferous beds very few organisms be- 
longing to groups other than the Graptolites occur, and 
none of these are characteristic shallow-water types. Over 
and above this, we find Graptolitic beds very commonly 
associated with rocks which, from their lithological nature, 
strongly suggest a deep-water origin. Ido not allude now 
to the Radiolarian cherts, but to such rocks as the bands of 
pale green mudstone associated with the “ Skelgill Beds” 
of the north of England, the “ Pale Slates,” red or green in 
colour, of the “ Browgill series” of the same area, and the 
grey or drab “Barren Mudstones” of the Ordovician rocks 
of the south of Scotland. All these are exceedingly fine- 
grained green, grey, or red muds, made up chiefly of de- 
composed volcanic material, often exhibiting stainings or 
dendrites of manganese, and nearly or quite unfossiliferous. 
The few fossils which they are known to contain are very 
small Brachiopods. It does not seem an unreasonable 
conclusion that these beds correspond with the “red clays” 
of modern deep seas; and this conclusion is rendered the 
more probable by the extraordinary persistence over large 
areas of even thin bands of the deposits in question. That 
such bands, occupying persistently a given paleontological 
horizon, must have been deposited with extreme slowness, 
hardly needs to be insisted upon; and each, though itself but 
a few inches thick, may represent a time equal to that 
required for the deposition elsewhere of hundreds of feet 
of coarse mechanical sediments. 
That the occurrence of Radiolarian cherts in rocks of 
older Palzeozoic age is not an isolated phenomenon is shown 
by the discovery of similar beds in the ancient rocks of 
Mullion Island in Cornwall, by Mr Howard Fox and Mr 
Teall (Quart. Jour. Geol. Soc, vol. xlix., p. 199, 1893). 
These cherts are in many respects similar to the Radiolarian 
cherts of Lanarkshire; and though, owing to the absence of 
other fossils than Radiolarians, the evidence as to their age 
is not conclusive, there is reason to think that they are of 
about the same horizon as the latter, and are of Ordovician 
