214 MINERALS AND GEOLOGY 



Of the microscopic forms, here separated under the name of Micro- 

 phytes from the Algce proper, the diatoms only are of palaeontological 

 interest representatives of the other groups being unknown, or only 

 doubtfully known, in the fossil state. The diatoms, which abound 

 in modern seas and in most fresh waters, secrete a siliceous test or 

 shell. Under the microscope, they present circular, stellate, triangu- 

 lar, sigmoid, and other shapes. Many siliceous deposits of cainozoic 



been forced to refer the impressions to four or five distinct species one impression being with- 

 out the lateral indentations. As stated by the writer more than ten years ago (Canadian 

 Journal, 1877 ; also, Annals of Nat. History, of the same year), the association of so many 

 different species, if the supposed tracks be really of animal origin, is at least a very remarkable 

 circumstance ; one, indeed, that might cause doubt in unprejudiced minds as to real nature 

 of these impressions. On the other hand, there is really nothing in them to conflict with the 

 view that they may be simply the impressions of large fucoids. Many of the existing Melano- 

 spermce grow to a great length : and in many genera with flattened or riband-like fronds there 

 is a well-defined midrib, sufficiently hard to make a distinct impression when the frond is 

 pressed upon damp sand. The lateral indentations of our Potsdam examples may have been 

 made by groups of spores or sporangia arranged (as seen in many existing sea-weeds) along the 

 sides of the fronds. Even apart from these, the air-bladders in many algae are capable of 

 making very distinct impressions on moist sand : and it would not be more unreasonable to 

 infer that in these ancient sea-weeds the spores were of a somewhat harder or denser nature 

 than to have to admit with Professor Owen that the crustaceans by whose feet the indentations 

 are commonly supposed to have been made, were "wholly distinct from the crustacean forms 

 of later geological periods or of the present day." 



If the impressions be fucoidal, the otherwise remarkable character of these lateral pit- 

 marks, in differing in number and grouping in different impressions, becomes easily explained 

 without the necessity of having recourse to imaginary specific distinctions. In the impressions 

 in which they do not appear, it may be inferred that the fucoid had already scattered its 

 spores, or that the development of the latter had not taken place, when the frond was cast 

 upon the ripple-marked shore of the old Potsdam sea. 



The supposed fucoidal origin of these impressions would not, I confess, however, have been 

 thus advanced, were it not for their association or connection in at least one locality the 

 vicinity of Perth, in Eastern Ontaiio with impressions of an analogous character to which an 

 animal origin can scarcely be attributed on any rational grounds. These are the impressions 

 known as Climactichnites. It is probable that the supposed animal origin of these latter 

 impreesions would never have been conceived, but for their general relations to the Protich- 

 nites impressions. They may be described, generally, as being in the form of a band, several 

 feet in length, although clearlj r fragmentary, with a width of from five to six inches. In their 

 general dimensions they agree, therefore, very closely with the Protichnites impressions. 

 But they differ from the latter in being traversed transversely by a series of narrow parallel 

 ridges, about an inch and three-quarters apart, and by having a kind of beaded edge or border 

 the impression, as remarked by Sir William Logan, thus somewhat resembling a rope-ladder, 

 whence the name Climactichnites. In some examples there is a central groove or ridge 

 running roughly parallel with the length of the impression. 



The points, here, to which attention should be chiefly directed, are, first, the presence of 

 these numerous transverse ridges ; secondly, their constancy, and the uniform clearness of 

 their outline, throughout the impression ; and thirdly, the unbroken continuity of the impres- 

 sion throughout its entire length. It must be evident that there are only two ways both 

 exceeding!}' improbable by which these impressions could by any possibility have been made 

 by any animal. If the impression be really a track, the animal must either have had, or have 

 been able to assume, the form of a complete sphere or cylinder with ribbed surface, and it 

 must have possessed sufficient internal force to roll itself over and over throughout a length of 



