154 GEOLOGICAL DISTRIBUTION. 



insects, the Lepidoptera and Hymenoptera, the two most highly 

 organised orders of insects, is noticeable. The only true trees, or 

 such as are made up principally of woody tissue, of the Carboni- 

 ferous deposits belonged to the coniferous series, the order of 

 plants which embraces the modern pine and its allies. These an- 

 cient evergreens were represented by several distinct genera — 

 Dadoxylon, Palseoxylon, Pinites — which, if the fossil fruit asso- 

 ciated with their remains, and known as Lepidostrobus, be justly 

 attributed to them, had their nearest allies among their modem 

 congeners in the ben-y-bearing yews. No deciduous leaf-bearing 

 trees, such as the oak, beech, or maple, which make up the great 

 mass of our forest growths, can be positively shown to have existed 

 in these early days. 



Permian Fauna, — In the formations of the period succeeding 

 the Carboniferous, the Permian, a considerable advance in the 

 structural type is indicated by the animal remains. While the 

 predominant forms of life of the period preceding pass, although 

 in most cases with very diminished numbers, into the present one 

 — in fact, to such an extent as to have induced many geologists to 

 unite the formations of the two periods into a common whole — we 

 meet here with a class of animals whose representatives had not 

 hitherto been detected. These are the true reptiles, most of whose 

 members belonged to the order Theromorpha (Pelycosauria), rep- 

 tilian forms which in several important characters — the sti'ucture of 

 the pectoral and pelvic girdles, humerus, and tarsus — show strong 

 affinities to the lower orders of mammals, the Monotremata and' 

 Edentata, of which, not impossibly, they may prove to be the early 

 progenitors. A further approximation to mammalian structure is 

 found in the character of the dentition, which in many forms ex- 

 hibits a distinct differentiation into incisor and canine teeth. The 

 deposits of the Southern and Western United States, especially of 

 the State of Texas, have yielded a wealth of species and genera 

 belonging to this order (Theropleura, Dimetrodon, Diadectes, Em- 

 pedocles, Clepsydrops), representative of several distinct families. 

 The modern type of lizards had their nearest analogues in the 

 monitor-like Proterosaurus (Germany, England), whose dentition, 

 however, was of the crocodilian type (thecodont). These early 

 reptiles, while exhibiting many points of structure indicative of 

 comparatively high specialisation, yet clearly proclaim a primitive 



