186 oN SOME TRACKS OF TERRESTRIAL AND FRESHWATER ANIMALS. 
and Crustacea made many of them. He referred to a description 
by Mr. Gray of the tracks of Gasteropoda. The mud-fans on the 
Norfolk coast offered excellent opportunities for a study of phe- 
nomena of this kind. He called attention to the burrows seen 
in the Assynt quartzites and the so-called fucoids. 
Rey. E. Hirt referred to the cracks in these muds, and agreed 
with the author that the worm-tracks help to produce them. 
Dr. Hicxs referred to the markings of Cruziana, and to some re- 
searches he made near Nant Ffrancon last summer. He had traced 
one for over 10 feet in length; some appeared to be even longer. 
He thought that they were relief burrows of worms produced in the 
manner described by Prof. Hughes. He agreed with Dr. Dawson 
that it was not safe to class any of these markings as plants 
unless they showed organic structure or retained carbon. 
Prof. Huenzs said that his object had been simply to describe 
some peculiar markings on mud, the manner of formation of which 
he had been able to observe, and to point out in what respects they 
explained away difficulties which had arisen in the interpretation of 
certain fossil tracks. He thought he had been able to show that 
some of the characters most relied upon to prove the vegetable 
origin of the fossil forms, such as branching, solid section, &c., could 
be produced by animals. He had seen the curious symmetrically 
branching grooves, due to streamlets on the sea-shore, mentioned by 
Dr. Dawson, and some tracks of “rustacea, such as those mentioned 
by Prof. Rupert Jones ; but he had been unable to preserve any of 
these owing to their being generally on sand, and also because they 
were obliterated by the succeeding tide instead of being left to dry. 
