Highest Goal-measures of Durham. 205 



or five faults that occur in it, includes a peculiar layer, 1£ inches 

 thick, of slickensided, broken up, and powdered shale, which 

 occasionally splits and does not maintain a constant horizon in the 

 shale (see Fig. 2). This disturbed band marks a plane of thrusting, 

 the beds above having moved on the upper layers of the shale, the 

 powdered and broken up material acting as a lubricant. It is 

 impossible to say whether the displacement is of large or small 

 magnitude owing to the faults which cut out the beds, but it seems 

 probable that the movement to which this slickensided layer is due 

 was produced by the same forces that caused the extensive series of 

 horizontal movements, which have been proved to have occurred in 

 both the Coal-measures and the Permian rocks of South-East 

 Northumberland and North-East Durham, 1 the results of which are 

 so well exposed in the Permian rocks of Claxheugh. 2 



These fossiliferous Coal-measures are the highest visible in the 

 northern coalfield. Those situated immediately under Sunderland 

 are inaccessible to research, and any evidence available from borings 

 or pit-sinkings can yield little palaeontogical evidence of value, but 

 it can be fairly safely asserted, that those that occur in this section 

 cannot be more than 50 or 60 feet below the top of the Coal-measure 

 floor, as it existed just previously to the deposition of the overlying 

 Permian. Also our knowledge of the lie of the coal-bearing rocks 

 beneath the east of Durham enables us to assert that they are near 

 the top of the highest Carboniferous strata, as these occur in 

 Northumberland and Durham. This zone, therefore, is of importance, 

 since it marks the upper limit of the Coal-measures of these 

 two counties. 



Evidence bearing upon the height of these beds above the chief 

 workable seams of the district has been obtained from details of the 

 sinkings at Hylton Colliery, which is situated about a quarter of a mile 

 to the east and Monkwearmouth Colliery about 2 miles in the same 

 direction. No intervening faults of any great magnitude occur. At 

 the former colliery the thickness of the Coal-measures to the main 

 coal of the "Wear is about 1,300 feet, and to the Maudlin or Bensham 

 seam about 1,375 feet, while at the latter the thickness to the main 

 coal is about 1,170 feet, and to the Maudlin 1,265. 



Near the top in the Hylton sinking some bands of clay ironstone 

 are recorded, which may very well be the same as those at 

 Claxheugh, as the beds dip gently in an easterly direction. 



Paleontology of the Claxheugh Beds (C. T. T.). 

 "Aneylus" Vinti, Kirkby. (PI. V, Figs. 1-4.) 



This problematical fossil occurs in great numbers in the layers of 

 clay ironstone. Generally the specimens are more or less crowded 

 together along certain bands in the rock to the exclusion of other 

 fossils, but occasionally they occur scattered about on the surfaces 

 that yield the bivalves of the group of Anthracomya Phillipsi. 



1 The evidence is detailed in " Stratigraphy and Tectonics of the Permian of 

 Durham " : op. jam cit., pp. 288-99. 



2 Op. jam cit., p. 159. 



