No. 385.] FORESTRY AND GEOLOGY. . 5 
destroyed the process of again enriching the soil is an exceed- 
ingly slow one. Fire-swept areas in the coniferous zone are, 
therefore, naturally barren for a much longer time than are simi- 
lar areas in the deciduous zone. A corollary to the foregoing 
propositions is that changes wrought within the limits of the 
deciduous or coniferous zones would not normally lead to such 
extensive changes in species as would be the case under similar 
circumstances within the limits of the tension zone. In the 
former instances the original species would be likely to reappear 
again, as their relatives would be their nearest neighbors. In 
the latter instance, however, any change might afford just the 
advantage which some species of one of the border zones 
required for their establishment in new territory. It is in the 
tension zone, undoubtedly, that the greatest change in species 
and in the limits of species, has occurred, especially since the 
advent of civilization, as it is there that cultivation has been 
extended over the greatest area. In the marl belt the original 
forest was destroyed at a very early period, on account of the 
value of the soil for farming purposes, so that we do not know 
just what was the original condition throughout that region ; 
but the indications are that coniferous trees were formerly 
more abundant than they are now, both in actual numbers and 
relatively to the deciduous trees; while in the bordering zones 
the relative proportions of the several species have probably 
always been about the same as now. 
In the following table an attempt has been made to give an 
idea of the general character of the forests in the deciduous 
and coniferous zones by listing the species which were found 
to be the most conspicuous and characteristic in each. 
DECIDUOUS (NORTHERN) ZONE. 
Gymnosperme : Pinus Strobus L., Tsuga Canadensis (L.) Carr., Juni- 
perus Virginiana L. 
Angiosperme : Juglans nigra L., Hicoria ovata (Mill.) Britton, H. glabra 
(Mill.) Britton, Æ. alba (L.) Britton, Carpinus Caroliniana Walt., Betula 
lenta L., B. lutea Michx. f., Fagus atropunicea (Marsh.) Sudw., Castanea 
dentata (Marsh.) Sudw., Quercus Prinus L., Q. rubra L., Q. coccinea 
ang., Q. velutina Lam., Q. alba L., Ulmus Americana L., Liriodendron 
tulipifera L., Platanus occidentalis L., Cornus florida L., Rhododendron 
