178 PROF. T. M‘KENNY HUGHES ON SOME TRACKS OF 
10. On some Tracxs of TERRESTRIAL and FRESHWATER ANIMALS. 
By T. M‘Kenny Hueuss, M.A., F.G.S., Woodwardian Professor 
of Geology, Cambridge. (Read November 21, 1883.) 
[Puates VIII—XI.] 
Tue ancient rock-markings known as “ Bilobites,” and afterwards 
described by D’Orbigny under the name of Cruziana, have long 
been known, and have proved a fertile source of controversy, some 
regarding them as plant-remains, and others looking upon them as 
traces of animals. A host of smaller, but similar markings, such as 
Rysophycus, or simpler forms, as Palwochorda, or the various very 
constant and symmetrical varieties known as Nereites and Myria- 
nites, or those with a more plant-like outline, as Chondrites, all 
belong to the same line of inquiry. Few writers on the Cambrian 
and Silurian rocks have not had to refer to what they called 
fucoidal markings, or worm-tracks, which often have their im- 
portance increased by being the only traces of life in the bed. 
Throughout the geological series to the present day, similar things 
are found. 
But though observations on the tracks made by recent animals had 
long ago been made by Emmons (American Geology, Pt. vi. 1857), 
and though Dawson had watched and recorded the various markings 
produced between tides on the long shores of the Bay of Fundy 
(Acadian Geology, p. 25), it has remained for Nathorst, in his 
splendid monograph on “Tracks of Invertebrate Animals” (K. 
Svenska Vet. Academiens Handlingar, Band xviii. No. 7), to place 
the whole question on a new footing by his experiments with living 
marine animals, and his extended observations on recent and fossil . 
forms, 
The very full bibliography given by him renders it unnecessary to 
refer more particularly to the various authors alluded to above; but 
in the following notes, which may be considered as supplementary 
to his, I give the results of further and different observations upon 
the manner in which the tracks of animals anastomose, terminate in 
foliated or branching heads, or stand out in relief with a solid section, 
—how the same animal may produce a dotted, unilobate, bilobate, or 
quadrilobate track, or a track in one place smooth throughout, in 
another place having strize oblique or almost parallel to the direction 
of motion, and in another strie at right angles to it. 
In the neighbourhood of Cambridge there is, at the base of the 
Chalk, a bed from 10 to 20 inches in thickness, which we eall the 
Cambridge Greensand, as there is uot quite sufficient paleonto- 
logical or stratigraphical evidence to justify our correlating it 
exactly with the Upper Greensand of other districts. This bed 
consists of a clayey shale full of glauconitic grains, phosphatic 
nodules, and phosphatized fossils ; all of which increase in quantity 
towards the base until sometimes the bed is quite green from the 
glauconitic grains, or black from the phosphates. As, however, 
