50 GEOLOGICAL MEMOIRS. 



the present flora or fauna of the same place, and from several 

 such local and temporary results draw conclusions regarding every 

 point of the earth's surface and all the shortest intervals of time 

 of one ' life of a species.' For this purpose we will review various 

 formations. 



a-e. For these, the oldest formations, it may suffice to refer to 

 our Enumerator in respect of the Plantee vasculares monocotyledo- 

 nese, some groups of Anthozoa, the Brachiopods, the Cephalopods, 

 the Trilobites, the Ganoids, and to remark that the numerous spe- 

 cies of most of these divisions have been made known from a small 

 number of localities during a period of scarcely ten years' search, in 

 order to produce the conviction that the earth in that period of time 

 was not poorer in species of the orders of plants and animals just 

 named than at present. 



h. The St. Cassian formation may belong to the II., or to m in 

 the III. period, but anyhow its series of strata bespeaks a limited 

 locality, a time of formation not longer than one of our ' lives of a 

 species,' and furnishes us with a sea fauna of more than 700 species of 

 invertebrate animals and sponges, corals, echinoderms and molluscs, 

 which is more than we are now able to collect from any similarly 

 limited space in the bottom of the sea. 



m. Whilst before the Lias we could not bring together a dozen 

 winged insects, this yields us in England not less than four species 

 of Libellulinse of three different genera, on the surface of one or two 

 layers of a marine deposit, in a district so limited that in the same 

 place at present, and that too on the land (where the Libellulse live), it 

 would perhaps be difficult to collect with all diligence as many living 

 species. The larvse of these animals in the water subsist on other 

 larvse ; in their winged condition they are continually catching other 

 flying insects for food, which there can be no doubt must have for- 

 merly existed along with them, even although we should not now 

 find them. In like manner the number of ganoid fishes belonging 

 to the Lepidoid and Sauroid families which may be found collected 

 in a single point in many localities in England is very considerable ; 

 for the quarries of lias-shale at Lyme Regis alone have furnished 8 

 genera with 22 species of Elasmobranchii, and 18 genera with 49 

 species of ganoids (which in the whole existing creation are repre- 

 sented by only 4 genera and 27-30 species). 



n^ In the forest-marble of Calvados in the communes of Ranville, 

 Luc, Lebisey, and Langrune, Michelin himself has found 67 species 

 of polyparia and spongiariee, whilst Ehrenberg, on the coast of the 

 Red Sea, where one-third of all the known coral animals live, could 

 not collect above 1 20 species, and perhaps the whole Mediterranean 

 would not yield ^1 species. 



n^. In like manner, Goldfuss has described from the Upper Jura 

 of Streitberg 45, of Giengen 1 7, of Nattheim 8, of Thurnau 7 spe- 

 cies of spongiarise and polyparia, without mentioning those also oc- 

 curring in these localities, but which had been already described in 

 other places. For in the whole Hartmann enumerates 80 species of 

 polyps from Wurtemberg alone, Goldfuss and Milnster 40 species of 



