238 Reports and Proceedings — Geological Society of London. 



2. " The Bajooian of the Mid-Cotteswolds." By S. S. Buckman, 

 Esq., F.G.S. 



The Mid-Cotteswolds is defined as the district between the valleys 

 of the Frome and the Chelt. A description of twenty-five sections 

 is given, dealing principally with the strata found between the 

 Upper Trigonia-grit and the upper Freestone — such strata being 

 called, for the purpose of present distinction, "the intervening beds." 

 Of these twenty-five sections, seventeen, lying between Stroud and 

 Leckhampton, are discussed in Part I of the paper to show the 

 succession of the intervening beds, to point out that Cotteswold 

 geologists have confounded two distinct deposits, the Lower Trigonia- 

 and Gryphite-grits, to prove that the former, and not the latter, is 

 the more persistent stratum, and to give evidence that denudation, 

 called " Bajocian denudation," has, prior to the deposition of the 

 Upper Trigonia-grit, cut right through the intervening beds in the 

 neighbourhood of Birdlip, so as to make a shelving trough six miles 

 wide and about thirty feet deep. 



. The remaining eight sections are described in Part II of the 

 paper. They lie eastwards of Leckhampton, and are given to show 

 the discovery of another ammonitiferous horizon in the Cotteswolds, 

 yielding angustumbilicate Witchellice. It is proved that this bed 

 is above the Notgrove Freestone and below the Upper Trigonia- 

 grit ; so that it is really an addition to the stratigraphical sequence 

 hitherto recognized in the Cotteswolds. Its ammonites show it 

 to have been deposited contemporaneously with the middle of the 

 Sandford Lane Fossil Bed, and yet it is removed by ten to twelve 

 feet from the Gryphite-grit=:lower part of that bed. In the Mid- 

 Cotteswolds this important Witchellia-hesiriug bed is only preserved 

 over an area of about 1^ square miles, because it has been mainly 

 removed by Bajocian denudation ; and only one side of one small 

 quarry yields a favourable exposure. No other locality showing 

 this deposit has yet been found in the county. 



Two plotted diagrams are given to show the developments of the 

 beds in the different sections, and to illustrate the result of the 

 Bajocian denudation. In an Appendix to Parts I and II various 

 notes are given, and attention is called to a remarkable oyster as 

 a document of historic value evidencing the Bajocian denudation. 



Part III of the paper gives the chronological sequence of Brachio- 

 poda in Dorset and the Cotteswolds in the Inferior Oolite, to show 

 their value for purposes of exact correlation when ammonites are 

 absent ; and to illustrate that the Brachiopods are a good medium of 

 exchange in regard to the strata of the Cotteswold and Dorset 

 districts respectively, that in some cases they are such in regard to 

 the two districts, and in other cases they fail in this respect, so 

 that ammonites become the only true medium of exchange between 

 the beds of different basins. 



An Appendix to Part III describes certain new species of 

 Brachiopoda, and gives notes upon others. 



