340 Mr. Weaver's Geological Observations on 



red colour, appears also occasionally of greenish and grayish hues, the same 

 mass of stone not unfrequently displaying them all together, separately or 

 intermingled. On the other hand, the clayey and marly beds in particular 

 abound with green and blue streaks, which intersect the strata in all directions ; 

 and irregular patches, spots, spheroidal and ovoidal nodules, possessing similar 

 colours, are scattered through them ; while in the cliffs may sometimes be 

 observed circular and oval rings of blue and green, as if laid on with a painter's 

 brush, being in fact so many sections of nodules possessing a different central 

 colour. These delineations and differences of colour, appear to be owing in 

 part to the variable state of oxidation of the iron, that enters into the com- 

 position of the rock. 



This range of old red sandstone is also partially exposed in other quarters, 

 e. g. at the town of Berkeley, in the Eastwood stream west of Stone, at Lob- 

 den quarry, and in various places extending toward the foot of Whitecliff, 

 Park ridge, and of Sunday's hill ; generally reposing in its eastern confines 

 unconformably on the transition tract. 



§ 18. The southern range of old red sandstone may be traced^ in conjunc- 

 tion with the carboniferous limestone, continuously through the elliptic ridge 

 from Chipping Sodbury on the south-east, past Wickwar, to Tortworth hill 

 their extreme point on the north, where the former obtains a thickness of 

 about 120 feet ; thence descending to the south-west into the vale of Fal- 

 field, rising again in Milbury heath, and proceeding thus along the inter- 

 rupted ridge that extends past Tytherington and Alveston to the Bristol Avon, 

 west of Clifton, being partially overlayed in its course by the newer sedimen- 

 tary formations. This elliptic ridge dips throughout towards the coal-basin. It 

 has been already remarked, however, (§ 6.) that the old red sandstone forms 

 in the northern part of Milbury heath an arched inflection, rising from the 

 south-east and inclining to the north-west : but along the western brow of 

 that heath, the sandstone is so much abrupted that the south-eastern inclina- 

 tion alone is visible. More south, in the projecting range that extends 

 westward towards the Severn, between Alveston and Thornbury, the arch 

 appears to be again complete, the sandstone supporting the limestone in a 

 conformable position, dipping to the north-west. It appears also, that such 

 has been the general arrangement in the line of prolongation toward the 

 Bristol Avon on the south-west; though the beds are greatly abrupted in their 

 course and partially concealed from notice : and a similar disposition is also 

 observable in these two formations in the vicinity of Pen Pole, not far from 

 the estuary of that river. 



§ 19. Confining our attention to the elliptic ridge with its inclosed basin, 



