As a general
rule, also, the Permian rocks appear to pass upwards conformably
into the Trias. The division, therefore, between the Permian
and Triassic rocks, and consequently between the Palaeozoic and
Mesozoic series, is not founded upon any conspicuous or universal
physical break, but upon the difference in life which is observed
in comparing the marine animals of the Carboniferous and Permian
with those of the Trias. It is to be observed, however, that
this difference can be solely due to the fact that the Magnesian
Limestone of the Permian series presents us with only a small,
and not a typical, portion of the marine deposits which must have
been accumulated in some area at present unknown to us during the
period which elapsed between the formation of the great marine
limestones of the Lower Carboniferous and the open-sea and likewise
calcareous sediments of the Middle Trias.
The Permian rocks exhibit their most typical features in Russia
and Germany, though they are very well developed in parts of
Britain, and they occur in North America. When well developed,
they exhibit three main divisions: a lower set of sandstones,
a middle group, generally calcareous, and an upper series of
sandstones, constituting respectively the Lower, Middle, and Upper
Permians.
In Russia, Germany, and Britain, the Permian rocks consist of
the following members:--
1.
Pages:
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302