PALAEOZOIC. 33 



jutting out on the hill-sides. In this respect they offer many 

 more natural exposures than do the Secondary and newer 

 strata, in crags and scarps, and along the sides or bottoms of 

 water-courses. These rocks are the principal repositories, in 

 England and Wales, of metallic wealth and of coal ; and 

 although not so tempting to the collector of fossils as many 

 of the newer strata, they must always command great interest, 

 because in them we look for the earliest traces of life on the 

 earth. It has been suggested that life originated in the Polar 

 Regions, on the grounds that the equatorial regions would 

 have been too hot to support life in the earliest geological 

 period.^ 



Concerning the oldest supposed evidences of Palseozoic vegeta- 

 tion, they are generally referred to Alga:. Indeed, the Cambrian, 

 Silurian, and Lower Devonian systems form the first botanical 

 epoch of Professor Schimper, to which he gives the name of the 

 " Period of Thalassophytes," because, with few exceptions, only 

 sea-weeds have been recognized in these formations. The term 

 Eophytic has also been applied. The evidence of the existence 

 of plants is based on certain markings on the surface of the 

 rocks, for rarely have any traces of structure, or even of carbona- 

 ceous stains, been noticed in connection with any of these supposed 

 AlgcE. The markings have received specific names, and have been 

 grouped into genera, but it is very doubtful whether there is sufficient 

 evidence to show that they are really impressions of plant-forms, 

 especially in view of the interesting observations of Dr. A. G. 

 Nathorst. He has noticed on the mud of the Baltic shores, 

 markings and impressions produced by the action of flowing water 

 on small obstacles, or on plants, which are identical with some of the 

 markings found on the surface of Palaeozoic rocks. ^ Some so-called 

 plant-remains may also be trails and burrows of Annelides. Dr. 

 Nathorst has shown that different animals may produce similar 

 trails, and the same animal different forms of tracks. He regards 

 Eophyion as probably the trail of Medusa, and PalcEochorda as trails 

 of Mollusca and Crustacea.^ 



The plants of the Upper Palaeozoic rocks are chiefly Crypto- 

 gams — Ferns, LycopodiacecE, and Eqtiisetacece. These range 

 from the Devonian rocks upwards ; but the earliest traces of 

 land-plants have been found in Silurian rocks. 



The Palaeozoic rocks contain many genera of Corals, such as 

 Helioliies, Favosites, Lithostrotion, Halysitcs, CyathopJiylliiui, 

 and Calceola ; and of Crinoids, as Actinocriims, Platycrmus, 



1 See Address to Norfolk Nat. Soc. i8S6, by Major H. W. Feilden. 



- W. Carruthers, Proc. Geol. Assoc, v. 4. See also G. Mag. 1883, p. 33. 



3 G. Mag. 1882, p. 22. See also T. McK. Hughes, Q.J. xl. 178. 



