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A 30 Structural and Physiological Botany. . 
presents the greatest similarity to it; but there are also 
points of resemblance to those of California, New Zealand, — 
and Australia. 
The next systems, the J/zocene and Pliocene, are se- 
parated somewhat arbitrarily from the preceding and from one 
another, if the floras only of the formations be considered ; 
the transition from one to another, and from these to the pre- 
sent, being quite gradual. We find, the higher we ascend in 
the Tertiary strata, an increasingly greater number of forms 
which indicate a cooler climate. The tropical plants gradu- 
ally disappear, and are replaced first by subtropical forms, 
and then by those adapted to a temperate climate. Especi- 
-ally in the Middle ‘Tertiary or Miocene system we find 
large masses of carbon deposited in the eartn in the form of 
beds of ‘brown coal’ or “zgnzte.. It is evident that the 
German deposits of lignite are almost entirely composed 
of the remains of Coniferze ; while in the mars, the sandy, 
loamy, and argillaceous strata which accompany the lgnite, 
a number of the impressions of exogenous leaves are 
always found. But these coniferous forests did not exhibit 
‘a dull uniformity, as is the case with those of the present 
time ; there was, on the contrary, an abundant and cheerful 
variety of forms, as is seen even now in the forests of 
Canada and Asia, though not to so great a degree. There 
must also have been enormous quantities of resin exuded 
by some of these trees, genera resembling Zhuwja and 
Cupressus, the preserved stores of which are eagerly sought 
for ; this resin, hardened by external conditions, being now 
known as amber. In addition to the Coniferze already 
mentioned, we find, in what appears to be near the close 
of the Tertiary period, that the forests of northern and 
central Europe consist largely of dicotyledonous trees—oaks, 
beeches, birches, alders, and willows. Plants belonging to 
the Primulacez, Scrophulariaceze, Crassulaceze, and other 
existing orders, sprung from the ground beneath the trees, 
covered with moss and fungi, and adorned with Rhododen- — 
