198 Mr. Maclauchlan's Notes to accompany a Geological Map 



brook, is cut out of the sandstone for the greater part, and is connected with 

 Bircham Wood. On the other hand, the occurrence of the conglomerate at 

 Bircham, when taken in connexion with the diversity of dip, supports the sup- 

 position, of an upthrow in this particular spot. 



The surrounding limestone dips regularly into the coal-field, and is ap- 

 parently undisturbed. 



It may be worthy of notice, that this conglomerate, at Bircham, forms, with 

 that at Buckstone on the north and Ailberton Common on the south, a line of 

 conglomerate nearly parallel to the general conformation of the coal-field on 

 the south-west. 



Near Ailberton Common, the dip of the old red is not always great, but 

 varies through every degree of inclination, and over a large part of the 

 surface, is less than 30°. 



The strata are often nearly or quite horizontal, and when that is the case, 

 a slight undulation makes the dip vary to quite a difi*erent point of the com- 

 pass, as is indicated by the arrows in the map. 



This nearly level position of the old red sandstone greatly increases the 

 difficulty, where it occurs, of distinguishing that formation from the new red 

 sandstone ; but in general, the upper beds of the old red are more highly 

 inclined than the lower ; though in the Tidenham Chase Hills, south of Hew- 

 elsfield, where such is the case, the mountain limestone conforms to the gentle 

 dip of the lower beds. Sometimes, the angle not even of the upper beds, is 

 great, particularly along the whole of the Ailberton Common district. 



In this country, the distinction mentioned in the Geological Transactions (2nd series, vol. i. p. 

 284,) between the middle and lower divisions of the old red, seems hardly maintainable. Corn- 

 stone nodules occur in the very lowest beds in the Severn Cliffs about Gatcombe, opposite the 

 transition limestone ; also in the cliffs on the left bank, between the outcrop of that limestone and 

 Sharpness Point ; and they are found at Blakeney. On the other hand, the flagstones are by no 

 means confined to the lower beds ; but are more common in those of the Mill Rough and the hills 

 west of Blakeney, in a higher part of the series than that in which any cornstone nodules occur. 



For a few miles east of Lydney, the country, for the most part, consists of 

 clay, except perhaps the upper beds along the Mill Rough and Horage Wood ; 

 but even in these locahties, the sandstone by no means exclusively prevails. 



The position of the small stone beds of the old red, sometimes varies sin- 

 gularly near the surface, lying thus, — ^ ^^^ -"^lo feet, "^^^^s^ , owing appa- 

 rently to unequal depositions. Such sections occur in the turnpike-road east 

 of Alvington, and some way east of Lydney. 



