REVIEWS AND BOOK NOTICES. 101 
tinguished by the abundance of some remarkable forms referred 
f the genera Spirophyton and Dictyophyton of Hall, 
also for the occurrence of vast quantities of humbly organ- 
ized acrogens suited for a semi-aquatic habitat, as Psilophyton 
and Annularia. May not these two la ps of plants be related 
in the way of derivation? Again the void thetic types of acro- 
gens of the lower Devonian, and the prototypal exogens of the 
genus Prototaxites give way in the middle Devonian to more 
perfect E be pitivette: types of acrogens and gymnosperms ; 
may they not have been advanced by a process of evolution? 
Such reit Aii have charms for persons of vivid imagination, 
and may be supported by the analogy between the progress 
favorable to algæ, and swampy flats favorable to Psilophyton 
and its allies, and by the alternation of these conditions in 
the same locality. Prototaxites does not change into Dadoxy- 
on. It disappears and is replaced by a type of wood which 
continues to the present day. Psilophyton continues to exist 
without improvement along with the Lepidodendra and ferns of 
of the gradual extinction of the old flora and the introduction of 
anew one from some different source. If therefore we desire to 
account for the succession of floras in this way, we must suppose 
local extinction and the introduction from another region of plants 
which in the meantime have been modified there 
In considering the relations of the Pre-carboniferous to the 
older floras, he considers that in accordance with the views that 
have been so well illustrated by Prof. Hall as to the derivation of 
the sediments forming the American Silurian strata from the north- 
east, and the gradual extension in each succeeding period of land 
and shallow water to the southwest we should expect to find the 
oldest land plants towards the northeast. ‘‘ Accordingly, it is in 
Gaspé that as yet we have the only link of connection of the Erian 
flora with that of the Silurian period,” i. e., the remains of a club 
moss (Psilophyton) ; and he believes that a by no means sparse 
land vegetation accompanied it. But he boldly inquires whether 
land plants did not exist in the Lower Silurian, and even hints 
that we might look for the actual origin of land vegetation in the 
