184 Geological Ohstrvations. 



tioii is displayed hy some such section as I have described. My 

 friend Dr. Prichard of Bristol informs me, by letter, that he has 

 observed the same nrrangement, /. e. the red sandstone dipping 

 under the limestone at the north part of the basin about Crom- 

 hall. 



Herefordshire and IV/onmcrjthshire, as I have remarked in my 

 former paper, exliibit<the same stratilication, which, according 

 to Dr. Prichard, continues into Brecknockshire*. Other writers 

 liave mentioned the same disi)osition of strata. It appears from 

 Mr. Bakeu-ell's section and account of the geology of Northum- 

 berland and Durham, in the Pi)ilosophical Magazine for Fe- 

 bruary last, that in crossing the ivland from tlie coast of Dur- 

 ham to the Irish Channel, the mountain limestone is inimediatelv 

 succeeded by the red sandstone. Mr. Aikin, in his account of 

 ihe great coal-field of Shropshire, says that the limestone, 

 which from its lying immediately beneath the coal can be no 

 other than tlie mountain limestone, is associated to a very con- 

 siderable extent with sandstone; and in another part he consi- 

 ders this sandstone as identified with the old red sandstone. 

 From these authorities it appears that the mountain limestone 

 is pretty constantly accompanied by the red sandstone, which 

 as constantly is situated helov.- it. I have little doubt that this 

 arrangement will be found still more general through the coal . 

 districts in England; but hitherto, mo^,t unfortunatelv, the red 

 sandstone has i)een perpetually confounded v.-ith the red marl, 

 and has been extravagantly considered as one of its beds f . WitJi 

 regard to the geological position of the red sandstone, there can, 

 i think, be but one opinion. It answers exactly to the descrip- 

 tion of the old red sandstone of Werner, and precisely resei.iiiles 

 the red sandstone in the neighbourhood of Edinburgh, and iu 

 the isle of Arran, which are considered by Professor Jameson as 

 characteristic localities of the formation in question. This opi- 

 nion, as I have jnst now mentioned, is distinctly stated by iVIr, 

 Aikin. If, then, this be the old red sandstone of Werner, the 

 first of the floetz series, we may fairly presume that the lime- 

 stone, 



* Vide Thomson's Amial-- for Jiir.e 181 j. 



t The siliceous pucldiiiii-sf.or.c, or more properly cofiglomerate, consistT 

 iug of pebbles of quartz fixerl in a basis of sandstone, wliich I ha\e de- 

 scribed as intervening between the red sandstone and limestone, is found, 

 «s I am inloiined by Professor Jameson, very generally accompanying tlie 

 red sandstone. It is by hiin considered merely a variety of tliis rock. He 

 is of opinion, that the rod sandstone is a pure chemical deposit, and that 

 the pebbles wliieh occur so abundantly in particular strata, arc to be 

 viewed not as the result of mechanical attrition, but as contemporaneous 

 v\iih the basis in which they are set, being formed by some particular nio- 

 ditication in the process of CTystallizntion, by which the siliceous particles 

 were attracted toj^ellier in the form of pebbles, instead of grains of sand.. 



This 



