of the neighbourhood of Bristol. 213 



flows over beds of white and red calcareous sandstone contain- 

 ing gypsum, which rests upon magnesian limestone. Now this 

 gypseous calcareous sandstone may be said to characterize the red 

 ground, therefore the magnesian limestone in that district may be 

 safely referred to that formation, and consequently may be regarded 

 as the rock next in succession to the Durham coal deposit. This 

 indeed might be collected from the imperfect sketch Dr. Thomson 

 has given us of its occurrence in that quarter. In a late number of 

 the Philosophical Magazine, it is said that the coal formation of 

 Whitehaven is covered at St. Bees Head by bituminous clay, over 

 this is a limestone containing magnesia and iron, and above this is 

 a red sandstone, connected with which is clay, marl, and gypsum. 

 This it will be perceived is almost an exact account of the succession 

 of the red ground strata in this quarter. In Derbyshire we are 

 informed that the magnesian limestone lies in an unconformable 

 and horizontal position over the inclined strata, after the manner 

 of its occurrence in this quarter, it therefore plainly belongs to the 

 same formation, the red ground. 



It may seem at first very remarkable that the basis of the lime- 

 stone conglomerate should be in one place merely a common lime- 

 stone, and that in another spot, not far distant, it should contain a 

 considerable proportion of magnesia. To those however who have 

 seen how widely the same rock formation, nay even the same 

 stratum, will vary in its colour, hardness, and general structure in 

 different parts of its course, this will cease to be a matter of wonder. 

 In attempting to explain these singularities, it seems to me that we 

 must resort to one of two suppositions : we must either conceive 

 that the fluid menstruum during the deposition of any particular 

 and extensive formation, must have contained in different places 

 different chemical ingredients j or we must conclude that the altera- 



Vol. iv. 2 E 



