Part of Gloucestershire and Somersetshire. 319 



Pyrton on the north ; the western side being formed by the left bank of the 

 Severn, and the eastern by a line drawn from Pyrton along the great escarp- 

 ment of oolite. Of the tract included in this area, I have represented in the 

 annexed map, only so much as, when combined with the sections by which 

 it is accompanied, may be sufficient to convey a clear idea of the relative 

 position and order of succession of the different formations. (See the Map, 

 Plate XXXIX., and Sections No. 1. 2. and 3. ; of which the Section No. 2. 

 occupies the whole base line of the triangle*). 



The structure of the north-west of Gloucestershire is illustrated by a sec- 

 tion drawn from Huntley-hill on the north-east, to the Forest coal-basin on the 

 south-west (see Plate XXXIX., Section No. 4.) ; and that of the north-west 

 of Somersetshire, by one general section (No. 5.), drawn from the Avon at 

 Bristol on the north, to the river Parret at Bridgewater on the south ; and by 

 a second section (No. 6.), traversing Mendip only, in the vicinity of Shipham. 



1. ENVIRONS OF TORTWORTH. 

 General View. — Secondary/ Formations. 



§ 4. One of the first impressions made on the mind, in examining the Tort- 

 worth district, is, that the existing form of the surface appears, to a certain ex- 

 tent, to be unconnected with the nature of the rocky formations that compose 



Lits base ; an observation, indeed, that may admit almost of universal applica- 

 tion, and be deemed a maxim in geology. A second impression is, that if 



.the distribution of formations into Primary, Transition, and Floetzf or sedi- 



[mentary classes, be well founded, — as resting on distinct epochs in the history 

 ind structure of our planet, the evidence of which is to be discovered in their 



[respective characters and relations; it is also true, that natural distinctions 

 point to a subdivision of the sedimentary formations, into collective series 

 or groups, consequent to, and in a great measure independent of each other, 

 with respect to the era of their production. Under this view, the first se- 

 ries of the sedimentary class, namely, the carboniferous, comprehends, in the 



* Having no map of Gloucestershire, that conveys an adequate idea of the form of the surface, 

 I constructed the annexed plan and sections of the environs of Tortworth from a survey, in which 

 my pocket-compass and clinometer were the only instruments employed. I trust, however, that 

 they will be found to represent faithfully the form of the country. 



+ The use of the German term Jlwtz is no doubt so far objectionable, as it does not har- 

 monize with our language : but in its full comprehension the word was intended to convey a com- 

 plex idea, for the expression of which we have not any corresponding English term, and to de- 

 note formations whose leading characters are, a distinctly stratified structure, combined with a 



VOL. VI. 2 T 



