318 ANNUAL OF SCIENTIFIC DISCOVERY, 



size, while in the latter period the converse holds. But during these 

 two reigns, Angiospermous plants appear to be wholly absent, or 

 are announced by a few rare signs, doubtful and very different 

 from existing forms. Each of these three reigns, thus characterized 

 by the predominance of one of the great divisions of the vegetable 

 kingdom, is commonly subdivided into several periods, during which 

 forms very analogous, belonging to the same families and often to the 

 same genera, are perpetuated ; then these periods themselves comprise 

 several epochs during which vegetation does not appear to have under- 

 gone any notable changes. But in many cases we are still without 

 materials for establishing these last subdivisions with precision, either 

 from the fact that the exact geological position of the strata which in- 

 close the impressions of the plants is not well determined, or that the 

 mode of distribution of the species of plants in the different layers of 

 the same formation has not been carefully made out. In accordance 

 with the knowledge we at present possess, I think that the three fol- 

 lowing general divisions of the vegetable kingdom may be admitted, 

 each divisible into epochs, during which vegetation preserved its in- 

 variable characters : 1st Division. Reign of the Acrogens, embrac- 

 ing the Carboniferous Period, not divisible into distinct epochs, and 

 the Permian Period, forming but one epoch. 2. Reign of the Gym- 

 nosperms, embracing the Vogesian Period, constituting one epoch, and 

 the Jurassic Period, with four epochs, the Keupric, Liassic, Oolitic, 

 and Wealden. 3. Reign of the Angiosperms, embracing the Creta- 

 ceous Period, with three epochs, the Subcretacean, Cretaceous, and 

 Fucoidian ; and the Tertiary Period, with three epochs, the Eocene, 

 Miocene, and Pliocene. M. Brongniart, in Annalcs des Sciences Na- 

 turelks, Vol. XL p. 285 ; and Magazine of Natural History, August 

 and September. 



ANALOGY BETWEEN ALPINE AND ARCTIC VEGETATION. 



THERE is no animal and no plant, which, in its natural state, is 

 found in every part of the world, but each has assigned to it a situa- 

 tion corresponding with its organization and character. The cod, 

 the trout, and the sturgeon are found only in the North, and have no 

 Antarctic representatives. The cactus is found only in America, and 

 almost exclusively in the tropical parts. Humboldt, to whom the 

 earliest investigations on this subject are due, extends the principle 

 not only to the distribution of plants according to latitude, but also ac- 

 cording to vertical elevation above the surface of the earth in the same 

 latitudes. Thus an elevation of 14,000 feet under the tropics corre- 

 sponds to 53 N. Lat. in America, and 68 in Europe. The vegeta- 

 tion on the summit of Mt. Etna would correspond with that of Mt. 

 Washington, and this again with the summits of the Andes, and the 

 level of the sea in the Arctic regions. In the ascent of a high moun- 

 tain, we have, as it were, a vertical section of the strata of vegetation 

 which " crop out," or successively appear as we advance towards the 

 north over a wide extent of country. But in dwelling on the resem- 

 blances between the plants of high latitudes and those of high raoun- 



