1853.] SALTER TRACKS IN THE LINGULA FLAGS. 209 



tion was frequently directed to very numerous evidences of the ex- 

 istence of marine worms during the formation of these ancient de- 

 posits. 



Nearly all the sandy and ripple-marked surfaces present worm- 

 tracks, whether in the higher or lower division of these strata, and 

 in all the localities visited : viz. the elevated country between Arenig 

 and Ffestiniog, the vale of Ffestiniog itself, and the valley of Tre- 

 madoc in Caernarvonshire. 



The latter locality, besides exhibiting a very complete section of 

 the whole series of these ancient rocks, exposes particularly well the 

 lower or lower middle portion, in which only the Lhujida Davisii is 

 found in any great abundance, but in which the Hymenocaris ver- 

 micauda also occurs. The latter fossil, a crustacean of the phyllopod 

 tribe, was described by m3 in the ' Reports of the Sections of the 

 British Association' for 1852. About a mile and a half west of 

 Tremadoc, the Lingula beds are well exposed ; and along the road 

 to Criccieth, and on the bye-roads near Penmorfa, they are loaded 

 with the Lingida ; — just above Penmorfa church the beds are parti- 

 cularly rich in this fossil. At the village of Y-Felin-Newydd, the 

 sandy surfaces are seen to be broadly ripple-marked ; and the beds, 

 alternately of coarse and fine materials — many different layers often 

 occurring in the space of an inch, — have quite the appearance of having 

 been accumulated near shore, or at least in shallow water. The 

 sandstone is highly micaceous in parts, often very fine-grained, 

 generally flinty and of a flag-like character, and, though not at all 

 cleaved, it exhibits everywhere proofs of movements which have com- 

 pressed the beds laterally and plaited their surfaces in a remarkable 

 manner. On one of the sandy surfaces, obscurely and broadly ripple- 

 marked, were a number of short parallel linear impressions, arranged 

 in several transverse curved series, and of such a uniform size and 

 character that it was plain they were the marks made in succession by 

 the same animal. (See figure, p. 210.) 



The space on the slab which these impressions occupy is more than 

 a foot in length ; and there are five or six distinct sets of indentations, 

 each set 3 or 4 inches in extent, and with a curved outline, the 

 broadest end of each impression being towards the outer side of the 

 curve. The indentations themselves are more than half an inch long, 

 and half a line wide ; abrupt and broad at their anterior end, and 

 tapering backwards to a point. They are almost always a little 

 curved, and are distant from one another a quarter of an inch, — in 

 some cases rather less, in others more. Intermixed with these, which 

 seem to have been the successive tracks of one larger animal, are 

 numerous similar series of much smaller size, and also many single 

 indents not placed in the regular transverse curves before noticed. 



That these are not the tracks of marine worms is at once evident 

 from their arrangement in regular series, and from their each tapering 

 backv/ards, as well as lying parallel to each other. The section of 

 each indent is subtriangular, so tliat it was probably made by some 

 sharp instrument ; and their shape tapering backwards and position 

 in parallel series indicate a rapid movement, such as would be given 



