322 Mr. Weaver's Geological Observations on 



The tract included in the area thus described, by following the line of the 

 overlying newer beds, from Wickwar, to Pyrton on the east, and from the 

 western escarpment of Milbury heath, to the vicinity of Berkeley on the 

 west, consists of rocks of the transition and carboniferous series ; which 

 are exposed to our observation by the interruption of that continuity, which 

 probably existed between the overlying sedimentary formations on the east 

 and the west, before the general surface of the country was moulded into its 

 present form, by partial abruption and denudation. 



§ 6. The general surface of the vales of the Avon and Falfield, is occu- 

 pied by a considerable depth of highly cultivated soil; but an examination 

 of those valleys, of the escarpments presented toward them and toward the 

 vale of Thornbury, and of the declivities and defiles, which lead from the el- 

 liptic ridge into the inclosed basin, has proved that portions of the transi- 

 tion and carboniferous series, together constitute a nearly concentric assem- 

 blage of beds; the northern limit of which is to be found near the confluence of 

 the river Avon with the stream of Falfield, and which is thence inflected to the 

 south-east, up the valley of the Avon, and to the south-west up that of Fal- 

 field. The dip is conformable to this arrangement, the strata on the north 

 being inclined toward the south, on the south-east toward the south-west 

 and west, and on the south-west toward the south-east; but toward the 

 head of the Falfield vafley they, are again inflected, gradually acquiring a 

 south-westerly inclination ; and in the old red sandstone a north-westerly 

 inclination also, the latter forming in that direction an arched curve, broken 

 at the surface, and therefore in this quarter so far unconformable to the tran- 

 sition tract. 



On the other hand, that part of the transition series, which borders the 

 flanks of the concentric assemblage at their northern extremity, pursues a 

 course more directly toward the north, preserving, where visible, a dip toward 

 the west, except at Pyrton Passage, where it appears in the form of an 

 arched inflection. 



This portion of the transition tract supports, and is bounded on the west 

 by a second range of the old red sandstone, which extends from the vicinity 

 of Pyrton in a south-west direction to the northern foot of Sunday's hill, in 

 strata variously inclined, and where visible on their eaetern boundary, gene- 

 rally unconformable to the transition beds. 



Such is the general disposition of the transition and carboniferous series in 

 this district ; but they display also occasionally inflections on a much smaller 

 scale, subordinate to and included in the general arrangement, being gently 

 undulated both in the line of range and of dip. 



