Tlte Carboniferous Liviestone of West Cumberland. 121 



(p. 81). Here the " pot-holes " are roughly cylindrical cavities in 

 the limestone, ranging in depth from 4 to 6 feet with an average 

 diameter of 2 feet throughout the greater part of their depth ; the 

 bottom is basin-shaped, whilst the top widens out rapidly to a 

 diameter of 6 to 8 feet. At Glints the cavity is filled with siliceous 

 shale or sandstone, and cavity and surrounding limestone alike are 

 overlain by an even-topped bed of sandy shale, a foot thick, above 

 which is an even bed of micaceous sandstone of about the same 

 thickness. Plant-impressions are abundant in the sandstone. 

 The cavities at other horizons are of various widths and depths. 

 The most notable occur in the white limestones at the base of the 

 Fourth Limestone, which form the passage beds from Dj to D... 

 The cavities are here found occasionally cutting clean through 

 one or two of the limestone beds, and forming a V-shaped " gutter " 

 or channel for some distance, which is filled with mottled shale or 

 mudstone. 



The cavities and " pot-holes " are invariably filled with shale, 

 sandstone, or rubbly limestone, and the next bed of limestone above 

 presents as its base a horizontal plane. In many instances pot- 

 holes are less than 6 feet apart. 



It is noteworthy that the " pot-holes " and cavities are overlain 

 by sandstones, in which the only organisms found are plants, or 

 by what appear to be algal limestones. For the only theory of 

 their origin that is adequate to explain their size and form is that they 

 are hollows eroded subaerially. They point, in fact, to repeated 

 incidents of emergence of the Carboniferous sea-bottom hereabouts 

 during upper D, and lower Dj times. The existence of true lime- 

 stone-breccia, lying at intervals in lenticular masses in the mudstone 

 which infils the channels, supports this conclusion. 



On the whole, the period was one of depression, that allowed 

 the accumulation of much lime-rock material ; but this depression 

 was interrupted by incidents of elevation of the Carboniferous 

 sea-floor, sufficient to bring it to the surface. The " pitted " 

 Limestones described by Mr. E. E. L. Dixon in his Gower paper 

 (p. 490) occur also in our area, and their origin may be similar to 

 the features described above. 



Fauna. 



The fossils listed in the tables and figures will be deposited in the 

 British Museum of Natural History at South Kensington, as will 

 also the larger collection at present in the possession of the author 

 and solely collected by him, when the listing is completed. 



Fossils are fairly abundant in the limestones, but recrystallization 

 has taken place to such an extent, especially in the massive beds 

 of the Fourth Limestone, that the brachiopods, lamellibranchs, 

 and gasteropods are difficult to extract, consequently good specimens 

 are rare. The corals taken from the carbonaceous shales in the 

 First Limestone are in a fine state of preservation, and afford good 



