208 Mr. Warburton o?i Magnesian Breccia. 



on the other side of the alluvial valley of the river Axe, and which 

 perhaps were originally continuous across the valley and rested 

 mediately or immediately upon the limestone ; but which have since 

 been removed by denudating causes, the hardest and most durable 

 part of their mass, the magnesian limestone, being left behind. 



I have heard of the following additional cases in which a mag- 

 nesian breccia is found in connection with red marl. Dr. Wollaston 

 in the first instance and afterwards Mr. Greenough informed me 

 that a similar rock was found near to Cowbridge in South Wales, a 

 specimen of which was presented by the latter to the Society. Mr. 

 Aikin also has noticed a breccia of the same description at Caerdeston 

 and Loton in Shropshire. 



In thus comparing the magnesian breccia of Bristol with the yel- 

 low limestone of the northern and midland counties, I have assumed 

 that the red marl which lies above the coal measures is of the same 

 order with that which lies at the bases of those escarpments, where 

 strata of mountain limestone are broken off; and where instead of 

 the lower beds rising from beneath the limestone we find horizontal 

 strata of red marl filling the plains. I am not prepared to establish 

 this by any positive proof; such evidence as the geology of the plain 

 of Carlisle would afford is already in the hands of Mr. Buckland ;* 

 the appearances that are to be sought after for determining this 

 question, and which perhaps may be observed in the neighbourhood 

 of Bristol, are the following : no disposition of the strata is more 

 common in the country between Bristol and the Mendip than that 

 described in Mr. Bright's paper ; where a ridge of mountain lime- 

 stone separates two plains from one another, each containing hori- 

 zontal beds of red sandstone or marl, the one lying above the lime- 



* See his paper, page 105 of the present rolume. 



