360 Mr, Weaver's Geological Observations on 



toward the west of souths supporting the limestone in a conformable position. 

 The latter rock continues to the southern declivity of the range ; where a 

 body of slate-clay makes its appearance, containing thin layers of limestone, 

 and also alternating with it in mass, 



§ 42. Let us now consider the general characters of the old red sandstone, 

 slate-clay, and limestone. 



In the lowest visible portions of the old red sandstone of Mendip occur 

 some beds of sandstone conglomerate ; and the common characteristics of the 

 formation are much the same as those of the environs of Tortworth and the 

 north-west of Gloucestershire; — with this exception, that clayey, marly, or 

 ' cornstone' beds are no where exposed to view, but layers of reddish slate- 

 clay, from six inches to one foot thick, are partially interstratified with the 

 sandstone. In this fundamental sandstone I have no where observed any 

 organic remains. 



The sandstone, where adjacent to the superincumbent slate-clay, is some- 

 times traversed by numerous small filamentous veins of calcareous spar, and 

 in some places it contains portions of carbonate of lime ; as in the Roborough 

 ravine, and in the road east of Winscombe church. And in the western 

 ravine connected with Burrington comb, 1 found its substance penetrated 

 with carbonate of lime to the depth of three or four fathoms ; the fracture of 

 the compound being compact, and of a blueish gray colour, while the exterior 

 coating appears as a yellowish, or reddish, friable sandstone, arising from the 

 loss of the carbonate of lime by weathering. 



The northern body of slate-clay, which, in the Burrington ravines, appears 

 to be about 150 fathoms thick, contains at first, incidentally, thin subordinate 

 beds of grayish and reddish sandstone and limestone, from one inch to two 

 feet thick, with which it alternates; but on approaching the continuous lime- 

 stone on the north, limestone becomes interstratified with it in thicker beds. 

 In this alternating series, a reciprocal incorporation of the substance of adja- 

 cent beds frequently takes place, either in a distinct form orindiscernibly; and 

 in all the varieties, minute scales of silvery mica are more or less disseminated : 

 but the purest beds of limestone in the slate-clay are found in the vicinity of 

 the continuous limestone, and the most sandy near the fundamental sandstone. 

 On the other hand, the interstratified beds of sandstone are seldom void of 

 carbonate of lime, except when in a partial state of decay ; constituting in 

 their sound state, a grayish firm compact rock, of a quartzy nature, and, in 

 the decomposed form, a yellowish or reddish sandstone, more or less coherent, 

 in which the casts and impressions of organic remains are particularly distinct. 

 The slate-clay is more partially penetrated with carbonate of lime, or with 



