Horace B. Woodward — On Landscape Marble. Ill 



■coincide with the uneven surface may be split from the rock. In 

 other instances the ridges on the surface are curiouslj'^ interlaced, 

 forming a kind of " rustic work " that is prized for rockeries. It 

 seems likely that the upper surface of the stone is largely due to 

 the shrunken state of the calcareous mud from which the Cotham 

 Stone originated. So far as I know, wherever the crinkly surfaces 

 and the arborescent markings are present, the limestone occurs in 

 isolated and lenticular masses ; and these are sometimes less than 

 a foot across, sometimes three feet or more. Where the stone, or 

 its equivalent, occurs as a fairly persistent layer, it maintains its 

 compact character, it is banded and evenly bedded, but the arborescent 

 markings are wanting. 



While the Cotham Stone is present in a number of localities from 

 Bristol to Uplyme in Devonshire,^ yet in many sections exposed over 

 that area it has not been recognized or but doubtfully identified, 

 partly because of its impersistent nature, and partly because it may 

 be represented by a layer without arborescent markings. This is 

 the case also in the country north of Bristol. 



It is interesting to find that this layer of limestone extends, even 

 in interrupted masses, over so large an area, and it is noteworthy that 

 wherever the characteristic Landscape Marble has been observed, it 

 occupies a position in the Ehastic Beds, at or near the junction of 

 the Black Avicula-contorta Shales with the overlying beds of White 

 Lias. The limestone thus forms an horizon of some service to the 

 geological surveyor, and it may be tracked across many a ploughed 

 field between Bath and the Mendip Hills. The finest examples of 

 the stone that I have seen, were opened up during the construction 

 of the Midland Railway between Bath and Kelston. 



To its stratigraphical position the Cotham Stone may in some 

 measure owe its peculiar characters, occupying as it does an inter- 

 mediate place between dark argillaceous sediments and almost pure 

 calcareous mud. In some localities a few inches of dark clay may 

 be found above the Stone, but usually it is overlaid directly by the 

 pale marls and limestones of the White Lias. It marks a stage 

 when this calcareous sediment was commingled with a slight amount 

 of dark mud deposited in occasional films. Thus an ordinary banded 

 limestone was produced in many places, as seen in the railway- 

 cutting *at Cossington, between Bridge water and Edington, at Aust, 

 and at Lassington near Gloucester. Beds of this character, although 

 they exhibit no arborescent markings, are often spoken of as "Cotham 

 Marble," because they occupy the same stratigraphical position. 



Between this ordinary banded limestone and the distinctly ar- 

 borescent types, all sorts of intermediate varieties may be found ; but 

 as most of these varieties are not ' ornamental,' they are regarded as 

 unsuitable for polishing, and do not come much into notice. Occa- 

 sionally in less compact rocks, where darker and lighter layers of 

 material are present, arborescent markings may be found ; this is 

 the case in the ' Estheria-hed,' which occurs in the upper part of the 



1 See Dr. Wright, Geol. Mag. 1864, p. 291. 



