268 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



divisions, and points out the large proportion which, in almost all 

 cases, divergency maintains to constancy. It shows also that the 

 weaker the vitality the less the divergency, as might have been 

 expected. Plants probably never diverge ; the one (Lycopodiaceous 

 spores) said to do so is supposed to be a land-plant, and anyhow only 

 occurs in finer or coarser forms of the same sediment. This Table 

 further shows that the species enjoying the widest geographical 

 range are the most divergent. 



For the purpose of more closely observing the mineral relations of 

 the fossils, the sediments (habitats) may be classed under two heads 

 — the "similar" and the '' dissimilar," each suiting particular fossils. 

 In the "similar" the characteristic ingredient remains predominant, 

 varying proportions of other minerals being introduced, as when 

 pure carbonate of lime becomes arenaceous or argillaceous. In the 

 " dissimilar" the characteristic ingredient disappears, or nearly so, 

 and is replaced by other minerals in varying quantities. We are 

 therefore not surprised to find that in Wales the number of 

 " divergents" entering similar habitats is 224, while those passing 

 into the " dissimilar" is 158. In I^ew York the difference is still 

 more striking, the proportion being 68 to 30. The fii'st or original 

 habitat niust be the oldest ; and it would be interesting to discover 

 the circumstances under which the transit from thence has been 

 made ; but such an inquiry is as yet in its infancy, and would 

 involve details on the habits of animal life, and on the effects of 

 oscillations in level, altogether out of place here. We shall only 

 say that many appear first in the sandstones of early Silurian times, 

 and ascend from thence into the muds and limestones of the eastern 

 and western hemispheres. We see this in Favosites alveolaris, 

 Stenojoorajlbrosa, Cornulites serpularius, Beyricliia KJoedeni, Athyris 

 reticularis, &c. 



Calcareo-argillaceous shale and calcareous sandstone seem to have 

 in Wales the most frequent organic relations with other sediments. 

 Speaking now of Welsh palaeozoic hfe, we find that the Bracliiopoda 

 are very divergent (see Table YI., Mineral Habitats). Orthis ele- 

 gantula occupies eleven habitats, and Strophomena depressa ten. 

 Much the same may be said of the Crustacea, while the Zoophyta, 

 with a few exceptions {Favosites alveolaris in 10 habitats), do not 

 often diverge. The Lamellibranchiata have considerable force in 

 this respect, but, with the exception of Pterincea retrojlexa, do not 

 enter very many beds. The same may be affirmed of the Gaste- 

 ropoda, — Cyclonema crebristria, Euomphalus funatus, and Platy- 

 schismus helicites, however, each frequenting seven habitats. The 

 Heteropoda are extremely divergent, Bellerophon bilobatus being 

 found in eight matrices. The Echinodermata seldom diverge. One 

 Annelid {Cornulites serpularius) is met with in ten separate beds; 

 but the rest seldom travel out of their first bed. 



After a very few necessary words on the divergency of the fossil 

 species of the New York Basin, in addition to what has already been 

 said, we shall content ourselves with producing Table X., intended 

 to show the comparative divergency of the fossil species of Wales 



