3*9 



RIPPLE-MARKED SANDSTONE AT 

 GRIMESTHORPE, SHEFFIELD. 



C BRADSHAW, F.C.S., 



Hoji. Sec. Sheffield Naturalists Club. 



The illustration on p. 320 is from a photograph of an excellent 

 example of ripple-marked sandstone, which occurs about two 

 miles to the east of Sheffield, in the grounds of the Grimesthorpe 

 Chemical Works, belonging to the Sheffield United Gas Light Co. 

 Limited. 



In this neighbourhood the geological horizon of the rocks is 

 chiefly that of the Middle Coal Measures, and the rippled stratum, 

 which has a dip of 27 towards the south, is one of the beds 

 occurring above what is known as the Parkgate Rock. The markings 

 in this fine-grained sandstone may be traced the whole length of the 

 northern boundary of the works' yard, a distance of some 1,450 feet, 

 the greater portion of which has been bared by the necessary 

 brickmaking and other operations of the Gas Company. An area 

 of the exposure, measuring 325 feet by 120 feet, has suffered little 

 as yet from the disintegrating effects of the atmosphere, and the 

 wave marks, which are nearly parallel to a line running east and 

 west, are remarkably sharp and regular, while here and there 

 transverse and longitudinal sections of Stigmaria are evidence of 

 the affinity between the rippled stratum, and the underlying coal 

 seams, of whose existence a contiguous pit affords practical proof. 



The illustration covers an area 26 feet by 20 feet, and besides 



the rippling it shows the preservation of what seems to have been 



a channel in the old sea beach, along which a streamlet, probably of 



fresh or brackish water, made its way across the shore to a shallow 



sea of the coal measure period. As this interesting feature does not 



appear to be of common occurrence in ripple-marked rocks, the 



illustration is taken from that part of the sandstone where it is 

 situated. 



In a short time atmospheric denudation will have obliterated all 

 traces of this sea beach of the coal period, but that there may 

 exist some permanent record of its occurrence, a slab 34 inches by 

 22 inches, kindly presented by the Gas Company, has been placed 

 in the geological collection at the Sheffield Public Museum. 



Thanks are due to Mr. T. Gascoigne Calvert, Superintendent of 

 the Chemical Works, for his courtesy in affording facilities for taking 



photog 



Oct. 1896. 



