THE SUCCESSION OF ANIMAL FORMS 



worms, obscure forms, which may represent crustaceans or 

 mollusks, markings of unknown origin, and some laminated 

 forms which may perhaps represent remains of Eozoon, though 

 their structures are imperfectly preserved. These are sufficient 

 to show that marine life continued in some forms, and to en- 

 courage the hope that a rich pre-Cambrian fauna may yet be 

 discovered. 



But let us leave for the present the somewhat isolated case 

 of Eozoon, and the few scattered forms of the Huronian, and 

 go on farther to the early Cambrian fauna. This is graphi- 

 cally presented to us in the sections in South Wales, as de- 

 scribed by Hicks. Here we find a nucleus of ancient rocks, 

 supposed to be Laurentian, though in mineral character more 

 nearly akin to the Huronian, but which have hitherto afforded 

 no trace of fossils. Resting unconformably on these is a 

 series of slates and sandstones, regarded as Lower Cambrian, 

 the Caerfai group of Hicks, and which are the earliest holding 

 organic remains. The lowest bed which contains indications 

 of life is a red shale near the base of the series, which holds a 

 few organic remains. The species are a Lingulella^ worm bur- 

 rows and a Trilobite. 1 Supposing these to be all, it is remark- 

 able that we have no Protozoa or Corals or Echinoderms, and 

 that the types of Brachiopods and Crustaceans are of compara- 

 tively modern affinities. Passing upward through 1,000 feet 

 of barren sandstone and shale, we reach a zone in which 

 many Trilobites of at least five genera are found, along with 

 Pteropods, Brachiopods and Sponges. Thus it is that life 

 comes in at the base of the Cambrian in Wales, and it may be 

 regarded as a fair specimen of the facts as they appear in the 

 earlier fossiliferous beds succeeding the Laurentian. Taking 

 the first of these groups of fossils, we may recognise in the 

 worms representatives of those that still haunt our shores, in 

 the Trilobite a Crustacean or Arachnoid of no mean grade. 

 1 Probably of the genus Olenellus. 



