MARKINGS, FOOTPRINTS AND FUCOIDS 323 



the tail, make double furrows with transverse ridges resembling 

 those of Bilobites, and there are even some mollusks which by 

 the undulations of the foot or the hook-like action of its an- 

 terior part, can make similar trails. A question arises here as 

 to the value of such things as fossils. This depends on the fact 

 that many creatures have left their marks on the rocks when 

 still soft on the sea bottom, of which we have no other indica- 

 tions, and it also depends on our ability to understand the 

 import of these unconscious hieroglyphics. They will certainly 

 be of little use to us so long as we persist in regarding them as 

 vegetable forms, and until we have very carefully studied all 

 kinds of modern markings. 1 Nor does it seern of much use to 

 assign to them specific names. The same trail often changes 

 from one so-called species, or even genus, to another in tracing 

 it along, and the same animal may in different circumstances 

 make very different kinds of tracks. There will eventually, 

 perhaps, arise some general kind of nomenclature for these 

 markings under a separate sub-science of Ichnology or the doc- 

 trine of Footprints. 



I have said nothing of true Algae or seaweeds, of which there 

 are many fossil species known to us by their forms, and also 

 by the carbonaceous or pyritous matter, or discharge of colour 

 from the matrix, which furnishes evidence of the presence 

 of organic material ; nor of the marks and trails left by sea- 

 weeds and land plants drifting in currents, some of which are 

 very curious and fantastic ; nor of those singular trails referred 

 to the arms of cuttlefishes and the fins of fishes, or to sea 

 jellies and starfishes. These might form materials for a 

 treatise. My object here is merely to indicate the mode of 

 dealing with such things, and the kind of information to be 

 derived from them. 



When we come to the consideration of actual footprints of 



1 Geologists are greatly indebted to Dr. Nathorst of Stockholm for his 

 painstaking researches of this kind. 



