PALAEOGRAPHY AND STRATIGRAPHY Tournaisian.—The Carboniferous period opened in western Europe with the northward advance of the pre-existing Devonian seas over the old Devonian land surface. In England and Wales, so far as is known, comparatively little of the present land area was submerged. The bulk if not the whole of Scotland either re mained dry land or was occupied by fresh water, and was the scene around Edinburgh of vigorous volcanic activity. In the south-west of England and in southern Wales the sea rapidly ad vanced to the southern edge of the ancient land mass of central England, and formed extensive deposits first of shales and then of crinoidal and dolomitic limestones extending from southern Wales through the Bristol area and across the English channel into Bel gium. The age of the thin deposits of culm shales and radio larian cherts found in Devonshire and Westphalia is rather un certain, although it is presumed that part at any rate of these beds correspond in age with the more normal Tournaisian beds with a brachiopod and coral fauna found in Belgium and Somer set. In northern England the middle and upper parts of the Tournaisian, although with a somewhat different fauna, have been found in the Lake District and in the Craven Lowlands of York shire, but the Tournaisian is absent in northern Yorkshire and Durham, Derbyshire and northern Wales. Towards the close of the period occurred a considerable local development of knoll reef (unstratified) shelly limestones (Waulsortian phase), seen as Waulsort in Belgium, Co. Clare and St. Doulaghs (Ireland) and Clitheroe (Lancs.) . The Tournaisian zones formulated by Vaughan, based on corals and brachiopods, are generally recog nized, and include : Marked by abundance of Caninia in specialized forms.
Marked by special brachiopods and zaphrentid corals. The Z equivalent beds in the Craven area of Yorkshire-Lancashire K are only feebly f ossilif erous, and the horizons have not yet been determined in detail.
In Ireland the basement shales and lower limestones of Cos. Clare and Sligo are of this age.
In western Europe the Tournaisian period is represented in its type locality the Tournai region of Belgium, but the unf ossilif er ous character of much of the Kieselkalk and Kieselschiefer of Westphalia makes the occurrence of beds of Tournaisian age in western Germany somewhat uncertain, unless one includes in the Tournaisian the beds with Protocanites at the extreme base of the Westphalian Carboniferous sequence. The exact correlation of the Pericyclus zones of Dr. H. Schmidt with the coral zones of Vaughan has not yet been accomplished.
The southern sea (the ancient Tethys) whose northern waters washed the southern part of central England in the Tournaisian period (with narrow gulfs extending farther north to Cumberland and Craven) is thus traceable by its deposits only obscurely through Germany towards Silesia. Marine deposits of this age reappear in central Russia (Kaluga), in the Urals and in the Kuznetzk coal-field in Siberia. Beds of this age may be present both in China and Japan, but their provenance appears doubtful.
In North America, according to Schuchert, "the submergence of Waverlian time began first in the Gulf States and along the west ern side of the Cincinnati uplift. At this early stage of the inun dation the seas were small in extent, but in Middle Kinderhook ian time the waterways were greatly expanded. The most strik ing change of the time, however, was the reappearance of the Cor dilleric sea, depositing far and wide throughout the Rocky Moun tains a great mass of limestones. . . . This Cordilleric sea . . . probably extended into the Arctic ocean." At the same period detrital deposits were being accumulated east and north of the Cincinnati uplift in the States of Ohio, Michigan and Pennsyl vania, with freshwater beds in the east (Pocono series) . In New Brunswick and Nova Scotia were deposited the arkoses and sand stones of the Horton and Albert formations.
No definite records of a Tournaisian fauna from the Southern Hemisphere appear yet to have been made.
So far as west European waters were concerned the sea life of this period appears to have consisted mainly of corals such as Caninia and Zaphrentis, brachiopods of the type of Productus burlingtonensis and Spiri f er konincki and crinoids. Goniatites were rare and local, being confined to the Protocanites beds at the extreme base in Westphalia and isolated occurrences of a Peri cyclus fauna as at St. Doulaghs near Dublin. There appears to have been a similar scarcity of goniatites in North America, and they are unknown in the southern hemisphere.
In southern Wales and Somerset the limestone sequence is more or less truncated at the top, there being no representative of the Yoredale Series except in Gower.
In Belgium the development is very similar to that of the coral-brachiopod facies of England, but in Westphalia the period commences with cherty shales and limestones and changes to fos siliferous platy limestones with a goniatite and Posidonomya fauna. Farther east, around Brilon, the beds are more shaly and remi niscent of the Bowland Shales. In Silesia the beds of this age included shales and conglomeratic sandstones of enormous thick ness, with a flora of Lower Carboniferous type and occasional goniatites and Posidonomya.
In Scotland the Lowland area (Ayrshire to Fifeshire) was still occupied by fresh water or an estuary, in which was laid down the Calciferous Sandstone Series and Oil Shale Group. Succeed ing these beds occur the Lower Limestone Group of Scotland, which consists of a series of thin marine limestones with thick in tercalated shales and sandstones, approximately equivalent in age to the uppermost Visean. The whole group thickens greatly eastward, attaining a maximum thickness in Fifeshire.
In Northumberland the sequence is similar to the Scottish one, and has been divided into a lower part (Tuedian) and an upper part (Bernician). The Tuedian consists of the Cementstone Group and Fell Sandstone Series of uncertain age, succeeded by a Coal Measure phase in the Lower Bernician. Succeeding this occurs the Upper Bernician with occasional thin limestones corresponding to the Yoredale limestones, and representing the upper Visean. Ireland was largely occupied by sea during this period, but the faunal sequence and correlation has not yet been worked out ex cept on the east coast near Dublin and in Co. Clare. Exposures at Great Ormes Head in northern Wales and in the south of the Isle of Man serve to connect the English Midland Province with the Irish sequence.
Seas of this period extended through Russia and Siberia to China and Japan and contained the same coral and brachiopod as semblage of fossils, which appeared again in the west of North America. A similar fauna is found in the Burindi Series of New South Wales. Towards the close of the period the localized abun dance of goniatites formed the most striking feature in the gen erally luxuriant marine life. The segregation of this goniatite and Posidonomya fauna into well-defined areas free from the Productid and coral fauna, is one of the most striking and curious features in Carboniferous oecology. It is clear that the separation of the two faunas was effected without recourse to any serious diastrophic movements such as the Poseidon Deep suggested by Schuchert to account for the differences in the American and European faunas. Indeed, the existence of such a Deep appears to be negatived by the identity of the Caney Shale fauna of Okla homa and the Bowland Shale fauna of Craven, coupled as it may be with the close similarity of the Nebraskan and Scottish lamelli branchs a little later. The goniatite fauna, abundantly preserved in Craven and probably in Ireland, in Belgium and Westphalia, and less abundantly in Silesia, occurs also in the Pyrenees, in northern Africa, and with traces as far east as Siam, and reap pears in great force in Oklahoma and the adjoining states of North America. It has not yet been recorded from the Southern Hemi sphere.
In North America the sediments of this period were less ex tensive than in the Tournaisian period. They consist in the Cen tral Interior area (of the United States of America) of limestones and oolites with sandy, calcareous shales on the flanks, and with beds of continental origin in the north-east. In New Brunswick, Nova Scotia and south-western Newfoundland occur narrow con nected troughs between mountain ranges, with conglomerates, sands, thin dolomites and gypsum. Shell-feeding sharks were es pecially abundant in North America at the opening of the period, and extensive fish remains have also been found at the top of the series in the Red Beds of the Yoredale Series near Leyburn (Yorks.). The following life zones have been generally recognized in western Europe :— The exact equivalence of the coral and goniatite zones has not yet been worked out.
The major grit beds are : (4) Rough Rock, of Gastrioceras subcrenatum age. (G) (3) 3rd Grit of Lancashire, of Reticuloceras bilingue age. (2) Kinderscout Grit, of Reticuloceras reticulatum age. (I) Grassington Grit, of Eumorphoceras age. (E) Of these four major grit invasions, the first or Grassington Grit reaches a maximum thickness near Burnsall, forms the Pendle Top Grit and caps many of the highest of the northern Pennine peaks. To the south it dies out, and is absent in Derbyshire. The Kinderscout Grit attains a maximum in the Peak District of Derbyshire, and gradually thins to the north being probably not more than 5oft. thick near Clapham (Yorks.) . The 3rd Grit of Lancashire has recently been proved by boring to thicken rapidly to the south-west, reaching a concealed maximum near Horwich (Lancs.) . These three grit invasions have maxima in distinct but adjacent territories of the deltaic basin, which appears to have been subsiding irregularly and disconnectedly. On the other hand, the fourth grit invasion (the Rough Rock) is known all over the Midland Province, and is fairly regular in its thickness. This fact, together with the immigration of freshwater mollusca into the area, suggest that depression and sedimentation were becom ing much smoother in action, and this is again reflected in the finer grain of the Lower Coal Measure sandstones. The thin coal seams of the Millstone Grit with their marine roofs are strongly suggestive of pauses in depression followed by a jerky subsidence which let in the adjacent sea (compare the buried forest bed and its marine roof in the Humber and other English estuaries in recent time).
At approximately the same period coarse detrital beds were laid down in many other areas in western Europe, but they no where appear to have been of the same coarseness and thickness as those of Lancashire, with the possible exception of the Silesian beds (of rather uncertain horizon). The source of the grit sedi ment of the Millstone Grit is not clear, as is also the exact mode of transport, but it seems probable that a northerly or north westerly source furnished the bulk of the sediment, and it is significant that the whole of the fossiliferous bands in the Mill stone Grit are marine (with the exception of one Carbonicola band near the summit). Similar grits occur in Newfoundland. It would appear that the Roslin Sandstone of Scotland is of approxi mately the same age, but the fauna is distinct and correlation is somewhat uncertain. The Flozleere Sandstein of Westphalia is of the same horizon as the Millstone Grit, and contains the same goniatite and lamellibranch succession.
Intercalated between the Grassington Grit and the Kinderscout Grit is an important series of marine shales, the Sabden Shales, containing many goniatite zones of upper E (Eumorphoceras), H (Homoceras) and (Reticuloceras) age. A similar shale series is present in Ireland (Foyne's island), Belgium (Chokier), and is partly represented in Westphalia, but in the latter area there is a slight suggestion of a sedimentation break, as several of the "H" goniatite zones have not yet been recorded. This sedimenta tion break was much more severe in southern Wales, where the earliest Upper Carboniferous goniatites so far recorded are of "H" age, and indeed the earliest goniatite is not uncommonly the basal goniatite of (Reticuloceras inconstans). At Haverford west the break extends up to where R. bilingue is the first zonal goniatite present above the break.
In Silesia the period is represented by the Hultschiner Schich ten and Ostrauer Schichten of the Sudetische Stufe.
The Lancastrian period in western Europe thus witnesses a great expansion in area of the goniatite fauna, and also of coarse detrital sediments. But the period has not yet been definitely rec ognized either in eastern Europe or America, except in the highest or Gastrioceras beds, which appear to have been very widespread. The major life zones represented are : G. Gastrioceras.
Reticuloceras inconstans and R. reticulatum (type form).
H. Homoceras (H. beyrichianum, etc.).
By reason of the marked change in the goniatite fauna, and the expansion which took place in the detrital deposits at the begin ning of the Lancastrian period, it has been suggested that the base of the Lancastrian division should be regarded as marking the inception of the Upper Carboniferous, as understood in Europe. It should, however, be pointed out that the change in the flora observed in Scotland occurs somewhat higher, namely, at or about the junction of the E and H goniatite zones. On the other hand, the Variscan mountain building commenced before the close of the Visean period, as here understood.
In Scotland the period commences with the Edge Coal series (perhaps the equivalent of the Grassington Grits), succeeded by the Upper Limestone Group (probably the equivalent of the Sab den Shales) and the Scottish Millstone Grit (perhaps the equiv alent of the Upper Sabden Shales and Kinderscout Grits). It is curious to note that the whole of the dominant and rapidly evolv ing goniatite genera are absent from the Scottish and North umbrian basins, the goniatites present in Scotland belonging to two closely allied genera, Dimorplioceras and Anthracoceras, of feeble ornamentation and sluggish evolution. It is this fact which renders correlation of the Scottish beds difficult.
In eastern North America the break between the Mississippian and Pennsylvanian is so profound that it seems probable that the lower part of the Lancastrian is missing. Colour is given to this supposition by the apparent absence of the lower and middle Lancastrian goniatites from the area. According to Schuchert, in the earliest Pennsylvanian "the seaways were small and restricted to Texas, Oklahoma and Arkansas, and long before the submer gence became general, three freshwater deltas were forming, one centring about Pottsville, Pa., another about the Kanawha river, West Virginia, and the third in the area of the Cahaba valley of Alabama. Finally these areas also came under the influence of the spreading seas at or before the close of Pottsvillian time. The submergence was most extreme in late middle Pennsylvanian time, when about 3o% of North America was again under the sea." Freshwater molluscs first became established in England towards the close of the period, when forms of Carbonicola oc curred abundantly at several horizons in zone G. The same is true of Westphalia and the Franco-Belgian basin.
In Britain occur the well-known adjoining coal-fields of York shire, Nottinghamshire, Derbyshire, Lancashire and Staffordshire containing amongst other seams the celebrated Barnsley and Silk stone coals. Of this age also are the coal-fields of south Wales, and there are minor coal-fields in Scotland, Northumberland (and Durham) and Somerset. In most of these there are occasional thin marine intercalations, which often form the roof of a thin coal seam. The major seams, however, have no marine roof, indicat ing that they were deposited during a period of tranquil subsi dence, and not during a pause in subsidence. In this connection one may observe that the enormously thick measures of Silesia contain correspondingly thick coal-seams. In Britain the produc tive measures are succeeded by the Upper Coal Measures of Staffordshire and southern Wales, which consist mainly of red marls and sandstones and are the highest Carboniferous beds in the British Isles.
Stephanian.—The highest Carboniferous beds of western Europe are those of the isolated basins in the centre and south of France, with a Pecopteris flora and abundant insect remains. It is possible that the highest beds of northern Staffordshire and southern Wales may represent this period, but there is at present no definite means of correlation. Approximately equivalent are the Ottweiler beds of Silesia and the marine limestones of the Urals containing Schwagerina. A Stephanian flora is found also in Spain and Italy, and there is a mixed Uralian fauna and Ste phanian flora, in the Carnic Alps. The Uralian sea was present in Asia Minor, Persia, India and China. In North America the period is represented by the upper productive coal measures of the Monongahela series and the Cisco formation of Texas.
The extensive "Permo-Carboniferous" glaciation of the South ern Hemisphere, and the succeeding Glossopteris flora of Gond wanaland, are now classed by the American geologists in the Permian system.
Europe generally during the Carboniferous period was divided into an eastern and western area of deposition by a land mass stretching from Scandinavia to southwest Russia. To the east and west of this land mass the conditions were very distinct. To the east a shallow brachiopod sea existed over the greater part of what is now Russia, with islands in the Urals, and this sea persisted dur ing the greater part of Carboniferous time, with somewhat diver gent conditions in the Donetz Basin. During the whole range of the period there were in this area few strong tectonic movements. In western Europe, on the other hand, during the Carboniferous period there began the great mountain-building movements called Variscan or Hercynian. These movements, which commenced in the Lower Carboniferous, were continued in Lancastrian and West phalian time with an energetic pressure towards the north. As a result, Middle Europe became a stable united land mass with great folds at the borders of the old Franco-Podolian ridge. This late Palaeozoic, augmented Franco-Podolian massif is termed by Bub noff the Middle European Ridge. Volcanic activity reached a considerable intensity; Scotland especially was the scene of great eruptions, remarkably well preserved. In Derbyshire submarine lava flows, now termed "toadstones," occurred, and in the area of the later Variscan mountains (Brittany, Central plateau, Vosges, Schwarzwald, Bohemian Massif) occurred great grano-dioritic intrusions.