The Geology of the Country Between Redcar and Bridlington
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THE GEOLOGY OF THE COUNTRY BETWEEN REDCAR AND BRIDLINGTON. By]. F. BLAKE, M.A., F.G.S.. President. (Read July srs, I89I) H ER E are two portions of the coast of England where one can T trace a continuous succession through the whole of the secondary rocks. One of these is in the south from Studland to Axmouth, the other in the north-east from Bridlington to Redcar. The contrast between these two is great. Although the com ponent members can be more or less continuously traced across the intervening space, the final terms of the series are more remarkable for their differences than for their resemblance. Throughout the whole succession we are in the face of two distinct types. The first endeavour of the Geologist is to assign the causes which have produced so remarkable a result. If we lay before us a geological map of England, and examine the structure of the Pennine chain, we see that in its centre-on the line that runs from Morecambe Bay to Flamborough Head-the Mountain Limestone comes up to the surface, and is surrounded on the north and south by Millstone Grit. In this phenomenon we have the first indication of a transverse anticlinal. This is shewn again by the separation of the Yorkshire from the Durham coal-field, through the rising of the Millstone Grit between them. The Permian follows suit. It is almost cut off as we trace it north wards, till it expands again on the other side of the Tees. In some maps, indeed, it is made entirely to disappear. Whether it actually does so or not, it rapidly changes character, so that its development in Durham is very different from what we find south of Yorkshire. Passing to the Trias, we find the Bunter sandstones to have quite disappeared (Mem. Geol. Surv., Sheets 96 N.W., and 96 S.W.), and the Keuper beds alone continuous from the Humber to the Tees. All these facts point to an upheaval of post-Carboniferous date along this line, which has had a separating effect on the areas to the east in the immediately succeeding periods. It was this old axis of elevation, which marked off the Yorkshire area through out Jurassic times. It was, indeed, depressed during the deposi tion of the Keuper and Trias, wherever they are clays-as we should naturally expect from the depth generally required to pro duce such rocks. But in the succeeding times it operated again. The Madstone, the Inferior Oolite, the Middle Oolite, and the Upper Oolite limestones, one after another, are seen to thin away as they reach the south of Yorkshire from across the Humber, and ,. N ... 84'1 ~Ul... JK.,tAClu~A: N_ 0'1 ~ ~s ",....! Peak. ';-< QJfC'f' L JIt'IE5f'tO/fIf€ :'l I"flO OLI t:l r ElJtul. Bay ;,. LOw e R ...... ;>1 M LO W e R ES T UAR I N E o Z .., ;I: M :>tJl>I o .z..,,vd Mo S ~ a 'Tj t:,iJM.,/u a lB n. ':''' ''':~;::'''':'if.'''f~l '~ r.lu:8.-w --=,",' '' i ''''! .' : G.l~ . ~. Oll rolilP C ....., ._~" J,' ''''''''': :>_':' ~ . FIG. I.-SECTION SEEN AI.ONG TH E CO AST OF YO RKSHIRE F ROM WHITBY TO FILEY BRIG.-J'. F. Bla ke. THE COUNTRY BETWEEN REDCAR AND BRIDLINGTON. II 7 the Great Oolite-even that most persistent bed, the Cornbrash dies away entirely; only the great clay deposit of the Oxford and Kimmeridge groups succeeds, as the other clays have done, in tra versing this dividing line. There was, therefore, a great physical barrier which separated the Yorkshire area throughout the whole period of deposition; and the basin thus formed was filled with material from different sources, and under different conditions from that of the larger area of the south. So much for the Jurassic rocks. Looking again at the geological map, in the area where the Trent runs eastward, we find that the Pennine chain and its ac companying Nottinghamshire coalfield come to a sudden end; and that beyond it, to the south, come great bosses of Mountain Lime stone, and the uprise of the older rocks in Charnwood Forest. This indicates a second transverse barrier, which had its first effect upon the Trias in the termination of the Bunter, and a later one upon the Jurassic in the estuarine character of the Great Oolites. But its effect was most marked in Cretaceous times; for north of this line, all sign of Gault and Greensand has disappeared, the Neocomian puts on a new aspect, and the Red Chalk begins to overlie it. The Chalk itself is tinged with red in its lower parts, and has occasional bands of clay, while the rest of the deposit is different in character, and no longer allows us to trace the persistent bands which mark off its subdivisions in the south. The basin thus bounded in Cretaceous times extends into Yorkshire, and thus its special characters are accounted for. After the abundant work that has been done upon this most interesting area by Phillips, Tate, Hudleston, the Geological Surveyors, Lamplugh, and the writer, there is little or nothing original to be said on this district, and one can only attempt to put into a connected form the knowledge already acquired. In tracing the upward succession of the rocks, we commence, of course, at the north. Here we find Triassic Marls which sweep round in a curve to the west, and form the boundary and basis of all that is interesting in the Secondary rocks of Yorkshire. Even these show a peculiar feature in the occurrence in them of a bed of rock salt 100 feet in thickness. This is found nearly at the base of the series, almost in contact with the Magnesian Lime stone, and Messrs. Lebour and Howse, of Newcastle, believe that it actually belongs to the Permian, or at least that some portion of it does. It is difficult, in fact, to say in this district where Permian ends and Trias begins, in spite of the absence of the Bunter. It may, indeed, be questioned, seeing that we have lost the Bunter, and gained in its place higher beds of Permian, whether one does not represent the other in time, the conditions of deposit having been different through their separation in different areas. However this may be, the occurrence of rock salt is interesting as indicating the physical conditions of deposit. It is not, indeed, on the same JI8 ]. F. BLAKE ON THE GEOLOGY OF horizon as the rock salt of Cheshire-which lies in the Keuper Marls, whereas this is at the base of theWaterstones-but it is an analogous formation. In Cheshire the salt forms lenticular masses, and there is every season to believe, from the sporadic nature of its occurrence, that it does so likewise in the Yorkshire and Durham area. Rock salt, from its great solubility, can only be formed where the sea either dries up or so nearly does so that the water is supersaturated. In either case the basin must be enclosed, and subject to much evaporation from its nearness to the atmosphere. This points to an elevation of the area and a cessation, for a time, of earthy deposits, and thus we find ourselves at the commencement of the formation of the Yorkshire basin. On the first commencement of depression we have the forma tion of the sandy Waterstones-thin bedded and even laminated, as though but little removed from the surface of the water; and these extend as far as the southern barrier. As the depression continues, we have the Keuper Marls widely spreading over the whole of England, and covering every older rock exposed; but still so confined beyond our area as to exclude the open sea with its abundant life. As the sea widens, the tea-green marls begin to denote a change, and with the black shales of the Rhretic we have the rash venturing of the outside forms of life into our area, and their rapid destruction as witnessed by the Bone bed. All these latter features are common to Yorkshire and the south of England. But after this, the northern barrier began to make itself felt, so that, though the sea was continuous over the whole of England, France, and Germany, during Liassic times, there are marked dif ferences in the minor lithological character between one locality and another. Commencing with the base of the Lias, we look in vain along the Yorkshire coast for any representative of the lowest zone, that of Am. planorbis. It doubtless occurs in the bottom of the North Sea, as proved by the constant washing up of hard calcareous nodules with this species (formerly called in Yorkshire Am. erugatus) in excellent preservation. Such specimens are never to be met with in the south of Yorkshire, on the other side of the dividing line. The zone is there well represented, but the specimens of Am. planorbis are more often of the slightly ribbed variety, and are flattened in the shale as in the south of England. The succeeding zones of Lias, those of Am. angulatus, Buck landi, and oxynotus, are well exposed at Redcar, and the two latter in Robin Hood's Bay. In these two localities they do not differ much in character. They present us with none of those smooth argillaceous limestones which have gained for the formation its name, but with a number of banks, each terminating upward in an indurated rough band, often filled with fossils, the most plenti ful of which are oysters of the form of Gryphea arcuata.