This order can be traced with certainty back to the early Jurassic epoch, while the Permian fossil Eugereon, and the living order - specially modified in many respects - of the Thysanoptera indicate steps by which the aberrant suctorial and piercing mouth of the Hemiptera may have been developed from the biting mouth of primitive Isopteroids, by the elongation of some parts and the suppression of others.
In those stems which have been referred with certainty to the Cordaiteae there is no centripetal wood; the spiral elements are adjacent to the pith, as in a recent Conifer or Cycad; certain stems, however, are known which connect this type of structure with that of the Lyginodendreae; this, for example, is the case in the Permian genus Poroxylon, investigated by Bertrand and Renault, which in general structure has much in common with Cordaiteae, but possesses strands of primary wood, mainly centripetal, at the (After Grand' Eury, modified.
The Trilobites are known only as fossils, mostly Silurian and prae-Silurian; a few are found in Carboniferous and Permian strata.
On both sides of the arch, east and west, the Coal Measures remain intact, forming outcrops which disappear towards the sea under the more recent strata of Permian or Triassic age.
He was distinguished for his researches on the Carboniferous and Cretaceous rocks and fossils of Saxony, and in particular for those relating to the fauna and flora of the Permian or Dyas formation.
Palaeozoic); Glossozamites and Pterophyllum among the Cycadales, and various vegetative shoots recalling those of the coniferous genus Voltzia, a well-known Permian and Triassic plant of northern latitudes.
Again, at the summit of the Carboniferous series, both the rocks and their fossil contents merge gradually into those of the succeeding Permian system, as in Russia, Bohemia, the Saar region and Texas.
From these beds up to the top of the Carboniferous there appears to be no break; but the Carboniferous beds were in some places eroded before the deposition of the Productus shales, which belong to the Permian period.
To the Permian period belongs a remarkable genus Eugereon, that combines hemipteroid jaws with orthopteroid wing-neuration.
In the outer portion of the zone the Permian and Mesozoic beds are crushed and folded against the core of ancient rocks; in the inner portion of the zone they rest upon the old foundation with but little subsequent disturbance.