212 Sir 4- Crkhton on the [March, 



In the present state of the world, the ratio of dicotyledonous 

 to acotyledonous and monocotyledonous plants is known to 

 increase (all other circumstances affecting climate being alike) 

 in proportion to the distance from tropical regions. In the 

 cooler regions of the temperate zones, the proportion is as 60 

 to 1. In the torrid zones as 5 or 6 to 1. But in the very ancient 

 world, all over the surface of the globe, we find nothing resem- 

 bling a dicotyledonous plant until we come to the oolite, 

 therefore, there is room to suppose that every part of the surface 

 of the earth at that period was hotter than our hottest regions. 



We now know from various facts that certain forms of vege- 

 tables and animals exist and multiply in a constant temperature 

 which approaches nearly to the heat of boiling water. Dunbar 

 and Hunter, in the journey they made along the river Ouachita, 

 in Luisiana, found bivalves, and confervas, and other plants, in a 

 hot spring, the temperature of which was between 40° and 50° 

 of Reaumeur's thermometer. Sonnerat and Prevost state, that 

 they discovered in the island of Lucon a stream of hot water of 

 6y° Reaumeur, and that the roots of the agnus castus and a spe- 

 cies of aspalatus grew in it. But a much more remarkable fact 

 is mentioned by Forster, who found living plants growing at the 

 base of a volcanic mountain in the island of Tanna, and that the 

 heat oCthe soil in which they grew was 210° Fahr. 



In the strata of the lias we meet with a rich collection of fossil 

 remains, but among them there are none which prove the exist- 

 ence of any one terrestrial quadruped. There are plenty of cro- 

 codiles, and we are introduced for the first time since the forma- 

 tion of granite to the Saurian family. 



Previously to entering into the consideration of these, it may 

 be observed, that the laws of animal life do not afford the natu- 

 ralist quite so certain a rule for judging of heat and climate as 

 plants do ; for every animal, from its being indued with a locomo- 

 tive faculty, can roam to a great extent in quest of food, and is 

 fitted to live where that can be found in sufficient abundance. 

 Nevertheless we know of many, the health and existence of 

 which force them to keep within certain boundaries of tempera- 

 ture. These, together with the antediluvian members of their 

 families, are the only witnesses that can properly be brought 

 forward to corroborate the testimony of the antediluvian flora. 



The examination of the analogies which have a reference to 

 this subject is attended with difficulty, and confessedly with 

 some want of precision, merely from the vague and loose manner 

 in which the denominations of the geographical zones are apphed 

 to the residence of animals. Some are described as inhabitants 

 of the torrid zone, others of the temperate zone, others of the 

 polar regions. In many cases, this is sufficient for general pur- 

 poses ; but as many genera and species of animals, both amphi- 

 bious and terrestrial, are confined to a range of from 12° to 20°, 



