as President, to the Geological Section. 465 



breccias and 'red beds,' they, in common with the Trias, must have 

 been deposited under fairly similar physical conditions in a sort of 

 Permo-Triassic lake basin. 



The bulk of the Trias, including the Dolomitic Conglomerate of 

 the Bristol district, is still regarded as of Keuper age, though it 

 is now admitted, as insisted on by Mr. Sanders years ago, that 

 the Dolomitic Conglomerate does not necessarily occupy the base of 

 the Keuper, but is mainly a deposit of hill- talus, which has been 

 incorporated with the finer deposits of the old Triassic lake as the 

 several Palteozoic islands gradually became submerged. The great 

 blocks which fell from the old cliffs were formerly regarded as 

 proofs of glacial agency, and there are persons who still believe, 

 more especially with respect to the Permian breccias, that such 

 rocks are indicative of a glacial origin. 



In the " Index Map " the Dolomitic Conglomerate and the Eed 

 Marl are thus included under the same symbol and colour. But this 

 is also made to include the Rhaetic — an arrangement which is hardly 

 in accordance with the facts observed in the Bristol area. On 

 a small-scale map so narrow an outcrop as that of the Rheetic 

 could hardly be shown ; yet its affinities are probably with the 

 Lower Lias rather than with the Trias. The late Edward Wilson, 

 whose recent death we all deplore, in his paper on the Rh^tic rocks 

 at Totterdown,' showed most clearly that the ' Tea-green marls,' 

 which had previously been associated with the Rhaatic, represent 

 an upward extension of the Red Marls of the Trias, in which 

 the iron had suffered reduction ; although there are indications of 

 a change of conditions having set in before the deposition of the 

 Rhsetics. The black RhEetic shales which succeed usually have 

 a sharp and well-defined base in a bone-bed with quartz pebbles, 

 etc., indicating a sudden change of physical conditions, though 

 perhaps no marked unconformity. In the South Wales district 

 the Rheetic limestones are said to be largely of oi'ganic origin and, 

 in addition to a Rhaetic fauna, to abound in the lamellibranchs so 

 plentiful in the lowest Lias limestones.^ 



The late Charles Moore always deplored the comparative poverty 

 of the Trias in fossils. In his last communication to the Geological 

 Society,^ he set himself to describe certain abnormal deposits about 

 Bristol, and to institute a comparison with the region of the 

 Mendips. He then suggested, on the faith of a sketch by 

 Mr. Sanders, that the famous Durdham Down deposit, already 

 inaccessible, might have been a fissure-deposit in the Carboniferous 

 Limestone like those at Holwell. He also stated that at one time he 

 had been inclined to regard the Reptilian deposit on Durdham 

 Down as of Rhastic age ; but the discovery of teeth of Thecodonto- 

 satirus, identical with those of Bristol, in a Keuper Marl deposit 

 near Taunton, induced him to refer the Durdham Down deposit to 

 the middle of the Upper Keuper. He had arrived at the conclusion 



^ Quart. Journ. Geol. Soc. , vol. xlvii (1891), p. 545. 

 2 Ann. Rep Geol. Survey for 1896, p. 67 (1897). 

 ^ Quart. Journ. Geol. Soc, vol. xxxvii (1881), p. 67. 



DECADE IV. VOL. T. NO. X. 30 



