ABSTRACTS OF LECTURES.
ST. AUSTIN'S STONE. BY THE REV. E. MAULE COLE, M.A., F.G.S.
St Austin's Stone, Drewton Dale, has naturally excited a good deal of attention. It is an exceedingly hard mass of chalk breccia, projecting from the side of a dale, towards the top. There is an exactly similar formation above the eastern entrance of Burdale tunnel, called the Fairy Stones. This latter rock extends for a distance of at least 100 yards on the surface in a westerly direction. Another notable instance occurs at High Towthorp. In this case the hard silicified rock can be traced for over 200 yards in a straight line across a field. At the western end there is a quarry with a good exposure of the rock face. For some ten or twelve feet down, the rock is very hard, below that depth the particles of chalk debris are loose and incoherent. Many other examples occur in other places, e.g. Wetwang, Fimber, Kirkby Grindalythe, etc. The ploughshare has to avoid such places. The width of these deposits varies, but the length in some instances, as at Burdale and Towthorp, is very far greater than the width. The suggestion is forced upon one that these were cracks, or fissures, or incipient dale-heads antecedently to the deposition of the breccia, into which the angular pieces of chalk and flint were pushed by some power, probably ice, moving over the surface. In process of time the rainfall acting from above as a solvent agent dissolved a certain portion of lime and silica, which on evaporation taking place, acted as a cement in building the loose particles together so firmly as to enable them to resist any further atmospheric denudation, at all events in comparison with the chemical wasting away of the surrounding chalk rock. Hence the projecting rocks at Drewton are a gauge to measure the amount of denudation which has taken place on the dale side since the said rocks were silicified. That the process of silicification began at the top and is still probably extending downwards is evident from the facts related above with regard to High Towthorp quarry. It is generally conceded that the Cleveland Hills, Moorlands, and Wolds were not surmounted by the great glaciers in the Ice Age, but they may have had an ice covering of their own, and if so that ice must have been in motion, more or less, and capable of pushing forward small chalkstones into any depression that came in its way.
The formation under discussion differs altogether from the conglomerates found on the top of the chalk at Sewerby, Danes Dyke, and other places; and from the Oolitic conglomerate found at Cart Naze, Filey. It is distinctly a breccia, not a conglomerate; the particles are very angular and have never been rolled or rounded by the waves. It seems to be purely a land formation. The Society is indebted to Mr. J. Pybus for lending the negative of the photograph forming the frontispiece and to Mr. W. S. Parrish for the prints of the same.
Copyright Hull Geological Society 2016