46 



THE CHAIN OF LIFE. 



specific forms strange to us. Perhaps the nearest approach to 

 such experience which we can make is to examine the group of 

 Cambrian animals delineated in Fig. 28, and to notice, under 

 the guidance of the geologist above named, the sections seen 

 at St. David's, in South Wales. 



Here we find a nucleus of ancient rocks supposed to be 

 Laurentian, though in mineral character more nearly akin to 



Fig. 28.— Group of Cambrian Animals (from Nicholson). 



a, ArcnicoUtes didymus, worm-tubes, b, Lingulella femtginea. c, Thcca Da7<idii. 

 d, Modiolopsis solvensis. e, Orthis Hicksii. /, Obolella sagittalis. g, Hymcn- 

 ocaris vermicauda. h, TrilobLte, Olenus micrurtts. 



the Huronian, but which have hitherto afforded no trace of 

 fossils. Resting unconformably on these is a series of par- 

 tially altered rocks, regarded as Lower Cambrian, and also 

 destitute of organic remains. These have a thickness of al- 

 most 1,000 feet, and they are succeeded by 3,000 feet more 

 of similar rocks, still classed as Lower Cambrian, but which 

 have afforded fossils. The lowest bed which contains indica- 

 tions of life is a red shale, perhaps a deep-sea bed, and possibly 



