244 Mr. Weaver on Floetz Formations. [Oct. 



old red sandstone being also wanting, the coal field reposes 

 simply on a transition tract: of which examples may be observed 

 in the coal fields of Shropshire. — (See Mr. Greenough's Geolo- 

 gical Map of England and Wales.) 



But, in general, in Great Britain, the three formations are 

 found in a more or less intimate state of affiliation, to illus- 

 trate which the following examples may be adduced, select- 

 ing only such as are characteristic of their various modes of 

 connexion. 



2. England. — That part of the old red sandstone of Herefordshire 

 and Gloucestershire (Group, No. 22 ofG. M), which supports the 

 forest of Dean tract, contains, incidentally, thin beds of lime- 

 stone, and, also, thin seams of imperfect coal. It is succeeded 

 by a belt of limestone, including beds of slate-clay (Group, No. 

 21 of G. M.), and supporting sandstone and sandstone conglo- 

 merate (Group, No. 19 of G. M.), which encloses the distinct 

 coal basin (Group, No. 18 of G. M.) of the forest of Dean. 



3. In the Environs of Tortworth, Gloucestershire, on the bor- 

 ders of the Cromhall coal basin, the old red sandstone alternates 

 with the limestone, while the coal formation is distinct. Such 

 appears likewise to be the structure of the western side of the 

 coal basin in Anglesea.* In both these cases, also, the imme- 

 diate foundation of the coal field is composed of the sandstone 

 and sandstone conglomerate, commonly called millstone grit y 

 which, in Ireland, is wanting in this position, the coal forma- 

 tion there reposing directly on the limestone. 



4. In the Durham and Northumberland tract, extending into 

 "Westmoreland and Cumberland, t the old red sandstone and the 

 limestone are found in repeated alternation with each other, and 

 with slate clay ; and the great coal formation is distinct, occupy- 

 ing the eastern quarter, and reposing immediately on sandstone 

 and sandstone conglomerate with slate-clay. But in the western 

 portion of the tract (where 21 beds of limestone are enumerated 

 as alternating with the sandstone and slate-clay), discontinuous 

 thin seams of indifferent coal are occasionally found, rarely 

 exceeding one foot, or at most 20 inches, in thickness. Of six 

 such seams of coal, which are noticed, the first (reckoning from 

 below upwards) occurs in the interval between the 1st and 

 2nd beds of limestone ; the second, between the 3rd and 4th 

 limestone ; the third and fourth between the 19th and 20th 

 limestone ; the fifth, between the 20th and 21st limestone ; and 

 the sixth, immediately below the 21st limestone. On the other 

 hand, in the northern portion of the tract (distinguished as group 



* See Mr. Farey in the Philosophical Magazine, vol. xliii. p. 126 and S26 ; and Mr. 

 Greenough's Geological Map of England and Wales. 



+ See the valuable papers of Mr. Winch and Prof. Buckland in vol. iv. of the Geol. 

 Trans, which, taken conjointly, place the relations of that tract in a luminous point of 

 view, and show that the series repose on transition, or on primary rocks. In this tract 

 I coincide with Mr. Winch, in considering as one the groups marked No. 21 and 20 in 

 Mr. Greenough's Map. 



