456 ; Geological Society. 
2. ‘The Base of the Devonian, with especial reference to the 
Welsh Borderland.’ By Laurence Dudley Stamp, D.Sc., A.K.C., 
F.GS. 
This paper is an attempt to establish a satisfactory base for the 
Devonian System, on a basis which shall serve for international 
correlation. The classification adopted is as follows :— 
Lower DrvonIAN (OLD ReDj II. Dittonian. 
SANDSTONE FAcrES.) 4 I. Downtonian. 
III. Ludlovian. 
SILURIAN (GOTLANDIAN)...... fe Wenlockian. 
I. Valentian. 
Murchison, in defining the Silurian System, drew the limit 
between it and the Old Red Sandstone below the Downton Castle 
Sandstone or Tilestones. He afterwards included the latter in 
the Silurian, and later writers have grouped still higher beds 
as Silurian. It is proposed to return to the original definition of 
Murchison. The Ludlow Bone-bed forms a natural base: it con- 
sists of fish-remains, all of which first appear at this horizon, and 
are genetically connected with higher Devonian faunas; it passes 
laterally into a conglomerate, and thus forms a natural physical 
base; it marks a paleontological and lithological break which can 
be correlated all over North-Western Europe. Typical sections are 
described in detail. 
A study of the paleontology of the Downtonian of the Welsh 
Borderland shows that the fauna of the lower beds (Ludlow Bone- 
bed, Downton-Castle Sandstone, and Platyschisma Shales) falls 
into three groups :— 
(a) Upper Ludlovian marine species which survived the change 
of conditions indicated by the bone-bed, and lived on in diminished 
numbers, but gradually die out. The Platyschisma Shales of Clun 
Forest are of deeper-water type than the Downton-Castle Sand- 
stone, and still other marine forms occur. 
(6) Species which flourished for a short time under the changing 
conditions. 
(c) New forms—chiefly fishes—which persist, or are closely 
connected with later Devonian forms. 
A comparison is made between the succession in the Welsh 
Borderland and various other regions:—Scotland, Devon and 
Cornwall, Northern France, the Ardennes, Britanny, Portugal, the 
Baltic lands, Spitsbergen, and North America. 
Some notes on the Downtonian paleogeography of England are 
added, and some remarks on the habitat of Devonian fishes. It 
is suggested, from the association of the early Downtonian fishes 
with marine invertebrates that they could live in either salt or 
brackish water, but gradually became specialized—some for a 
lacustrine habitat, others, perhaps, for marine conditions. 
