461 W. A. E. USSHER ON THE CHRONOLOGICAL VALUE OF THE 



the upper part of that subdivision is frequently represented by cal- 

 careous sandstones with so few contained fragments that the term 

 conglomerate can only be truly applied to the beds to within from 30 

 to 50 feet of the base of the subdivision. 



The same gradual change seems to have taken place in numerous 

 places between Tallaton and Thorn St. Margaret's, as considerable 

 difficulty is frequently experienced in fixing the upper boundary of 

 the pebble-beds, owing to the downward passage of sand, through 

 sand-beds in which pebbles are sparsely disseminated (false bedding 

 is frequently indicated in their linear arrangement), to pebble-beds 

 proper. 



This difficulty has almost led me to regard the pebble-bed subdi- 

 vision as an impersistent variation of the base of the Upper Sand- 

 stone ; but the prevalence of faults renders such a conclusion far from 

 certain. There can, however, be little doubt that the pebble-beds 

 and conglomerates are old beaches which heralded the deposition of 

 the Upper Sandstone, and were formed through a shoaling of the 

 Triassic sea-bed, or through access to materials not before ob- 

 tainable. 



When we consider the isolation of the Triassic area of the mid- 

 land counties from that of the south-western during the deposition 

 of this upper-sand series, the absence of identical constitution is 

 most natural ; but the points ^of similarity are abnormally striking : 

 compare, for instance, the following statements of Professor Hull with 

 those which I have just given regarding the early part of the Upper- 

 Sandstone period. 



In the Peckforton-Hill district *, Cheshire, the Lower Keuper 

 Sandstone is composed of : — 



1. Waterstones 150 feet. 



2. Hard red and white sandstones 200 „ 



3. A base of " hard calcareous breccia or conglo- 1 



merate, full of current-bedding, and resting I 



on a thin band of marl " J 50 „ 



Kidderminster and Bridgenorth districts f : " The basement-beds 

 of the Keuper in this, the typical district, consist of bands of marl 

 and ealcareous conglomerate passing into breccia." 



Wolverhampton, near Penn and Oreton Hills : " The basement- 

 beds of the Keuper consist of red marls and hard calcareous sand- 

 stone with pebbles." 



South and east of Stourbridge J the basement-beds of the Keuper 

 " may be regarded as an old shingle beach." 



" The introductory stage of the Keuper series was the formation 

 of a second shingle beach, very largely developed in Shropshire and 

 Worcestershire, but in a less-marked degree all over the central 

 counties" §. 



At Bull Hill ||, rock fragments, generally subangular and of small 

 size, " pervade the beds from the base upwards for about 200 feet." 



* Mem. G-eol. Surv. on Triassic &c. of the Midland Counties, p. 77. 

 t Ibid. p. 70. % Ibid. p. 69. 



§ Ibid. p. 107. || Ibid. p. 69. 



