Lancashire, Westmoreland, the Eden Valley, and in the East of England from Sunderland to Nottingham, there occurs a succession of limestones, sandstones, clays and other rocks with occasional beds of rock-salt and gypsum, which represent the various forms of sediment and chemical precipitates formed on the floor of Permian lakes. The poverty of the fauna and flora of Permian strata points to conditions unfavourable to life; and there can be little doubt that the characteristic red rocks of St Bees Head, and the creamy limestones of the Durham coast are the upraised sediments of an inland salt-water lake. The term Dyas was proposed by Marcou for this series of strata as represented in Germany, where the rocks are conveniently grouped in two series, the Magnesian limestone or Zechstein and the red sandstones or Rothliegendes. The older and better known name of Permian was instituted by Murchison for the rocks of this age, from their extreme development in the old kingdom of Permia in Russia. Unfortunately considerable confusion has arisen from the employment of different names for rocks of the same geological period; and the grouping of the beds varies in different parts of the world. It is of interest to note, that in the Tyrol, Carinthia, and other places there are found patches of old marine beds which were originally laid down in an open sea, which extended over the site of the Mediterranean, into Russia and Asia. In Bohemia, the Harz district, Autun in Burgundy, and other regions, there are seams of Permian coal interstratified with the marls and sands. From these last named beds many fossil plants have been obtained, and important palaeobotanical facts brought to light by the investigations of continental workers. Volcanic eruptions, accompanied by lava streams and showers of ash, have been recognised in the Permian rocks of Scotland, and elsewhere.

In North America, Australia, and India the term Permo-Carboniferous is often made use of in reference to the continuous and regular sequence of beds which were formed towards the close of the Carboniferous and into the succeeding Permian epoch. The enormous series of freshwater Indian rocks, to which geologists have given the name of the Gondwana system, includes the sediments of more than one geological period, some of the older members being regarded as Permo-Carboniferous in age. These Indian beds, with others in Australia, South Africa, and South America, are of special interest on account of the characteristic southern hemisphere plants which they have afforded, and from the association with the fossiliferous strata of extensive boulder beds pointing to widespread glacial conditions.

VIII. Trias.

As we ascend the geologic series, and pass up to the rocks overlying the Permian deposits, there are found many indications of a marked change in the records of animal and plant life. Many of the characteristic Palaeozoic fossils are no longer represented, and in their place we meet with fresh and in many cases more highly differentiated organisms. The threefold division of the rocks of this period which suggested the term Trias to those who first worked out the succession of the strata, is typically illustrated over a wide area in Germany, in which the lowest or Bunter series is followed by the calcareous Muschelkalk, and this again by the clays, rock-salt, and sandstones of the Keuper series. In the Cheshire plain and in the low ground of the Midlands, we have a succession of red sandstones, conglomerates, and layers of rock-salt which correspond to the Bunter and Keuper beds of German geologists. These Triassic rocks were obviously formed in salt-water lakes, in which from time to time long continued evaporation gave rise to extensive deposit of rock-salt and other minerals. From the fact that it is this type of Triassic sediments which was first made known, it is often forgotten that the British and German rocks are not the typical representatives of this geological period. The ‘Alpine’ Trias of the Mediterranean region, in Asia, North America, and other countries, has a totally different facies, and includes limestones and dolomites of deep-sea origin. “The widespread Alpine Trias is the pelagic facies of the formation; the more restricted German Trias, on the other hand, is a shallow shore, bay or inland sea formation[60].”

In the Keuper beds of southern Sweden there are found workable seams of coal, and the beds of this district have yielded numerous well-preserved examples of the Triassic flora. A more impure coal occurs in the lower Keuper of Thuringia and S.-W. Germany, and to this group of rocks the term Lettenkohle is occasionally applied.

In the Rhaetic Alps of Lombardy, in the Tyrol, and in England, from Yorkshire to Lyme Regis, Devonshire, Somersetshire, and other districts there are certain strata at the top of the Triassic system known as the Rhaetic or Penarth beds. The uppermost Rhaetic beds, often described as the White Lias, afford evidence of a change from the salt lakes of the Trias to the open sea of the succeeding Jurassic period. Passing beyond this period of salt lakes and wind-swept barren tracts of land, we enter on another phase of the earth’s history.

IX. Jurassic.

The Jura mountains of western Switzerland consist in great part of folded and contorted rocks which were originally deposited on the floor of a Jurassic sea. In England the Jurassic rocks are of special interest, both for geological and historical reasons, as it is in them that we find a rich fauna and flora of Mesozoic age, and it was the classification of these beds by means of their fossil contents that gained for William Smith the title of the Father of English Geology. A glance at a geological map of England shows a band of Jurassic rocks stretching across from the Yorkshire coast to Dorset. These are in a large measure calcareous, argillaceous, and arenaceous sediments of an open sea; but towards the upper limit of the series, both freshwater and terrestrial beds are met with. Numerous fragments of old coral reefs, sea-urchins, crinoids, and other marine fossils are especially abundant; in the freshwater beds and old surface-soils, as well as in the marine sandstones and shales, we have remnants of an exceedingly rich and apparently tropical vegetation. This was an age of Reptiles as well as an age of Cycads. An interesting feature of these widely distributed Jurassic strata is the evidence they afford of distinct climatal zones; there are clear indications, according to the late Dr Neumayr, of a Mediterranean, a middle European, and a Boreal or Russian province[61]. The subdivisions of the English Jurassic rocks are as follows[62]:—

JurassicPurbeck beds Upper Oolite.
Portland beds
Kimeridge clay
Corallian beds Middle
Oxford clay, with Kellaways rock
Great Oolite series Lower
Inferior Oolite series
Lias

In tracing the several groups across England, and into other parts of Europe, their characters are naturally found to vary considerably; in one area a series is made up of typical clear water or comparatively deep sea sediments, and in another we have shallow water and shore deposits of the same age. The Lias rocks have been further subdivided into zones by means of the species of Ammonites which form so characteristic a feature of the Jurassic fauna. In the lower Oolite strata there are shelly limestones, clays, sandstones, and beds of lignite and ironstone. Without discussing the other subdivisions of the Jurassic period, we may note that in the uppermost members there are preserved patches of old surface-soils exposed in the face of the cliffs of the Dorset coast and of the Isle of Portland.