192 Correspondence—Mr. Walter Keeping. 
imperfect excavations, would lead to the belief that only a few 
thousand years have elapsed since the glacial beds were laid down. 
The same conclusion can be drawn from the good preservation of 
the glaciated surfaces, and of the shells and bones on the terraces. 
Similar evidence is afforded by the rate of recession of coasts and 
waterfalls, and by the condition of eskers and lake ridges. If we 
adopt the shorter estimates afforded by these facts, it will follow 
that the submergences and emergences of land in the Glacial Age 
were more rapid than has hitherto been supposed, and that this 
would react on our estimate of time by giving facilities for more 
rapid denudation and deposition. Such results would render it less 
remarkable that no new species of animals seem to have been intro- 
duced since the Glacial Age.” D. MackinTosu. 
ON SILURIAN PLANTS FROM CENTRAL WALES. 
Sir,—In the January Number of this Magazine is a communica- 
tion from Dr. Nathorst on the Silurian ‘ Plants ” of Central Wales, 
in which he disputes the conclusion expressed in my paper on the 
“Fossils from Central Wales,”! as to the nature of the plant-like 
structures there described. In his opinion the Buthotrephis major, 
B. minor, Paleochorda tardifurcata, and Nematolites Edwardsti, are no 
plants at all, but merely the “trails and burrows of Annelids” such 
as he has lately obtained from worms placed on a surface of mud 
and plaster. 
It is difficult to understand how such a conclusion could be arrived 
at from my description; for taking first the species of Nematolites, 
these are described as ‘solid bodies of pale chocolate colour,” per- 
fectly separate from the dark shales in which they occur, and from 
which they can be readily removed with a penknife. Such a struc- 
ture can be no mere impression nor the filling up of a trail of worms 
or crustaceans, and I can think of nothing more probable than the 
suggestion in my paper that it is a Coralline Alga. In the second 
species, N. dendroidea, the lateral branching is tree-like, diminishing 
in size in a way impossible for aworm track. Also the Buthotrephis 
major are no filled up tracks and trails. They are thin surface 
structures, or impressions on the shales and slates, very regular in 
their form and branching, and the main stem is straight and regular, 
about two or three inches long and in no case resembles or passes 
into an ordinary worm track. Also they do not generally occur in 
association with the worm markings which are so abundant in the 
grits. Many of these latter are, ] have no doubt, tracks similar to 
those obtained by Dr. Nathorst, and to others which I have observed 
in the Cambridge slough-ponds at the coprolite diggings, but the 
Nematolites and Buthotrephis are quite distinct from these, and I can 
only refer them to the vegetable kingdom. 
Lastly, referring to my new species Myrianites Lapworthii, I have 
no hesitation in maintaining that name, to designate a group of well- 
defined markings agreeing perfectly with each other, and very dis- 
tinct from their nearest allies. Water KeEepine. 
1 Grou. Mac. November, 1882, p. 485. 
