I40 Chapman, Tracks made by Bittium cerHhium. [vok'> 



Nat. 

 XXIX. 



left in a moist condition by the retreating tide which had 

 evidently ebbed away a few hours l)efore. The patch under 

 observation measured about 20 yards by i yard, and was 

 covered with a network of shallow grooves about 3 mm. in 

 diameter, and about 1.5 mm. deep in the centre. There were 

 many other patches of a like nature in the surrounding area. 

 At the terminus of each long trail, and partly ensconced under 

 a little tumulus of sand, lay a living Bittium cerithiuni. The 

 mollusc in each case was slowly working its way along as it fed 

 on the organic particles, amongst which, no doubt, foraminifera 

 were included, for they were common in the sand. In its pro- 

 gression the mollusc tumbled the damp sand to each side, the 

 result of which was to form a fairly smooth groove, the edges of 

 which were raised slightly above the general surface of the sand. 

 From our observations at this spot it is probable that there 

 were many hundreds of these little Gasteropods at work^ some 

 of whose silent testimony of conditions in the human period of 

 the twentieth century may eventually be handed down to a 

 future school of geologists. 



In Palceozoic rocks similar tracks are not uncommon, and 

 when these are filled with a cast of mud the latter are often 

 erroneously referred to as sea-weeds or fucoids. In the Hudson 

 River group (Upper Ordovician) of North America, from Wash- 

 ington Co., Dr. J. Hall figured some trails under the generic 

 name of Gordia. These represent casts of slight depressions of 

 a meandering character, distributed over the surface of slabs of 

 shale, which that autljor compared with the tracks '' made by 

 Melania and other aquatic and marine shells of the ])resent 

 day."* The Palcdochorda minor and P. major. M'('oy,f of the 

 Skidtlaw slate, England, were probably due to the same cause — 

 that is, by the passage of Gasteropods over the wet sand. These 

 are referred by M'Coy to plant remains. 



The above are a few of many instances where similar trails 

 liave been referred, sometimes to animal life, at otiiers to plant 

 life. It is, therefore, a subject worthy of more detailed study 

 than has yet l)een given lo it, and by gathering similar facts we 

 may draw therefrom more certain inferences as to tlu^ nature of 

 many hitherto jnizzling organic remains. 



("oKKFXTiON. — The number of the volume on the cover of 

 the December Naturalist was i)rinted XXX. instead of X.XIX. 

 Will readers kindly make the necessary correction ? 



* Tal. New York, vol. i., 1847, p. 2^14, pi. Ixxi.. figs, i, .?. 

 I J'.iil Pal. I'oss., pi. i.\, figs, i-_^. 



