194 



ON SOME TRAILS AND HOLES FOUND IN ROCKS 



Martin, in his Petrificata Derbiensia, figures this shell as 

 conchyliolithus helicites, (pusillus plate 25,) and states it to 

 be of rare occurrence in the coal shale near Chesterfield. 

 The occurrence of it near the last-named town, in the lower 

 part of the middle division of the coal field, I can fully con- 

 firm ; but it is far from rare, being there met with in consi- 

 derable abundance. Sir Roderick Murchison, in his Silurian 

 System, at p. 84, in speaking of the limestone found in the 

 higher part of the coal field near Shrewsbury, states, — "That 

 the characteristic fossil of the limestone is a very minute 

 discoid univalve, resembling on first inspection jplanorbis nau- 

 tilus, Fleming, and with it is a small bivalve resembling a 

 cyclas." 



At p. 88 of the Silurian System, Professor John Phillips, in 

 describing the Ardwick limestone, states, — "Among the shells 

 the most characteristic is a microscopic spiral shell of few 

 volutions, which touch one another like the planorhis when 

 young, but when old are exhausted into a free tube like 

 vermetus, or rather like vermilia. The shell is sinistral like 

 jplanorbis, but sometimes shews proof of its being attached on 

 one side like spirorbis — lines of growth strong, somewhat 

 irregular, deficient in parallelism, and oblique to the axis of 

 the tube as in planorhis ; faint spiral striae can just be seen. 

 This shell, which I have identified with your Salopian 

 planorboid shell, is also probably the same as a species I have 

 seen from the coal measures of Fitzgerald's colliery,* near 

 Manchester, as well as from the lower part of the Yorkshire 

 and Newcastle coal field." 



Dr. Hibbert,f in noticing this fossil, states that it appears 

 in a crushed and broken state. In this form they exhibit a 



* After many years' search I have certainly found the fossil at this place, but 

 In nothing like the abundance as at the Bradford and Clayton collieries, where it 

 occurs in great profusion. 



+ On the Freshwater Limestone of Burdiehouse, &c. Transactions of the 

 Boyal Society of Edinburgh, vol. xiii., part 1, p. 180. 



