20 ON CERTAIN VERMIFORM FOSSILS. 



and comparatively incous2>icuous, and the sand is thrown up on 

 one side into an arched or rounded ridge (a), which sometimes 

 almost obliterates the furrow. The ridge itself is frequently 

 broken up into nodules (fig. 4), thus giving to the whole track a 

 beaded or articulated appearance. At each articulation a punc- 

 ture is occasionally observed in the furrow. 



These tracks, as just described, may be observed by any one 

 who will take the trouble to look for them; but it is not quite 

 so easy to determine how and by what they are formed. It was 

 long before I could ascertain these facts, and they were at length 

 determined only after some careful watching ; nothing, however, 

 is required but time and a little perseverance. The complication 

 and extent of the tracks are the main difficulties ; on this ac- 

 count it is impossible to keep in view at the same time all their 

 numerous windings, and in most cases the extremities are not to 

 be seen. I therefore went down to the beach, just as the tide 

 was leaving the spot where the broad or first described tracks 

 were usually in great profusion. The sand was quite smooth, 

 all irregularities having been obliterated by the action of the 

 water. Here and there, however, the tracks had already made 

 their appearance, but w^ere as yet of very limited extent, and 

 there was now no longer any difficulty in taking the Avhole in at 

 one view ; and, moreover, the extremities were perfectly distinct. 

 It was only necessary to watch attentively to note the formation 

 of the numerous and labyrinthine windings that had been so long 

 a puzzle. I had not to wait long before the sand at one of the 

 extremities was observed to be gently agitated, and on this 

 agitation ceasing the track was found to have added nearly half 

 an inch to its length. In the course of two or three minutes the 

 sand was again put in motion, and the track once more a little 

 prolonged. These movements were repeated over and over again, 

 until it was quite clear that the tracks were formed by slow, 

 intermitting steps, and not, as might have been supposed, by one 

 continuous, gliding motion. Having ^tisfied myself of this, I 

 took up the morsel of sand at the end of the track, just as it was 

 again becoming agitated, and found that 1 had captured a small 



