PERSISTENCE OF GENERA IN TIME. 451 



by the strata, nothing probably is more astonishing than the evidence 

 afforded of the way in which the principal types of life have persisted 

 on the earth. This correspondence between the ancient life and the 

 existing life was first enunciated in recent times by Professor Huxley. 1 

 It has been shown that the Lepidodendron of the coal-measures in all 

 essential details of structure is closely allied to the living Lycopodium. 2 

 Species of Araucaria are known from the oolites which also con- 

 tain species of Pinites, while the cretaceous rocks yield species of 

 Cedrus, pandanaceous fruits, Juglans (walnut), and a multitude of 

 other genera which still exist, and are met with throughout the 

 Tertiary period. This history is repeated by almost every group of 

 animals. The foraminifera of the Carboniferous period, together 

 with many extinct types, include existing genera (see p. 479). Among 

 the alcyonarians, the fossil Hdiolites makes a remarkable approxima- 

 tion to the surviving Heliopora. The great existing divisions of 

 sponges date back in time to the oldest rocks ; while the Mollusca are 

 for the most part represented at the present day by genera in which 

 the generic characters have remained unchanged through all geological 

 time. The Nautilus ranges through all strata. The Loligo com- 

 menced with the Lias and lives on to the present day. Among 

 gasteropods, Patella, D&ntalium, Trochus, Natica, Chemnitzia, are 

 common genera which all date back at least as far as the middle of 

 the Primary period. The bivalve shells tell the same story, Area, 

 Avicula, Lucina, Cardium, Pinna, Pecten, are all types which date 

 from the Primary epoch. Among brachiopods, Crania, Discina, 

 Lingula, Rhynclionella, and Terebratula are genera met with plentifully 

 in early Primary rocks. Among Annulose animals the Carboniferous 

 rocks have yielded scorpions, spiders, centipedes, and representatives 

 of the chief groups of insects and Crustacea. Nor are the vertebrata 

 an exception to this general law of the antiquity of life, for the oldest 

 fishes belonged to living groups, and the Elasmobranch and Ganoid 

 groups of the Palaeichthyes date from before the middle of the Palaeo- 

 zoic period. The Amphibia at their first appearance present a higher 

 type in some respects than any which now survive. The Crocodilia, 

 Chelonia, and Lacertilia, date from the secondary epoch ; and in the 

 older Tertiary rocks serpents are found, differentiated as in existing 

 groups. The few slight indications of birds found in the Cambridge 

 Greensand, combine in one type characters of divers, grebes, and 

 penguins ; while even the Mammalia in their oldest forms show, as 

 far as can be judged from a few bones in the lower oolites, and a few 

 teeth from the Trias, the essential organisation of existing marsupials. 

 We therefore discover that on the hypothesis of evolution, geological 

 history does not carry us back appreciably towards the origin of the 

 great divisions of organic nature ; or even towards the origin of the 

 chief generic groups. Hence it becomes rather a matter for wonder 

 that the changes in life should have been so slight with the successive 

 physical circumstances which have changed the distribution of land 



1 Royal Institution: Friday, June 3, 1859. 



2 Carruthers, Royal Institution, April 16, 1869. 



