350 SEWARD: FOSSIL CLIMATES. 
widely separated latitudes, all yielding identical species. His 
re briefly as foll i 
point to the Coal Period as one iiatekie a moist ar warm climate, 
the land more insular than in subsequent periods, a atmosphere 
more highly charged with carbonic acid gas. We uld find, did 
time allow, that this is in the main the view held be most vee the older 
botanists or se Sai “ie indeed, one which finds a place in some 
of our modern text 
In 1833, Witham published his work on ‘ The Internal Structure 
of Fossil Vegetables.’ Here is followed a new line of inquiry; the 
absence or very slight development of annual rings of growth in the 
wood of Carboniferous trees, their existence in Jurassic Conifers, 
indicating in the former period a uniform temperature without 
sharply defined alternations of seasons, in the latter a succession of 
periods of rest and of active growth, which have left their mark in 
autumn and spring wood. This annual ring test is further taken up 
by Lindley and Hulton in their ‘ Fossil Flora,’ and is well worthy of 
careful investigation to-day by those interested in paleoclimatic 
. questions. 
rof. Renault, of Paris, notes the superiority of plants over 
animals as tests of climate, the former, without the means of loco- 
motion possessed by the latter, being more susceptible to temperature 
changes 
r. As chibald Geikie and other writers lend their support to 
this view, that in ae rather than animals we, have the best 
thermometers of the past. 
Si arles Lyell emphasises the serious difficulty igo 
deductions as to temperature from fossil plants. On th older 
types—which in species, and even in genus and family, differ from 
present day forms—we can rely but little. We must be careful in 
case—i.e., in all geologic periods—to take into account the 
absence of competitive forms of a higher grade, whose presence in 
more recent times has doubtless played a most important part as 
a factor in — distribution. 
s ing of the earlier calculations as to the Coal Period 
climate, Lyell notes a modification in the opinions of botanists, 
ormerly in favour of a tropical temperature. Quoting such cases aS 
the Mammoth, whose thick and warm coat Cuvier regarded as 
a protection against Arctic cold, he suggests that this power of 
adaptation may have been possessed by those Carboniferous plants 
whose remains are preserved within the Arctic circle. We are 
Naturalist. 
