372 MR. E. S. COBiSOLD ON THE [vol. lxxvi, 



Horizon Ad. Lapworthella Limestone. 



The fauna of the Lapworthella Limestone, Ad, is as follows : — 



Species. Remarks. 



Acrothyra cf , sera Confined to this horizon, but represented by a near 



ally, A. comleyensis, in the Paradoxides Beds. 



Lapworthella nigra Confined to this horizon. 



Hyolithellus micans Ubiquitous, both above and below. 



Hyolithellus micans var, Now found for the first time, and passing up into 



robustus. the Paradoxides Beds. 



Helenia cancellata Found in the Lower Cambrian, from Ac,, but not 



above this horizon. 



Certain trilobitic (?) Found also in the Protolenus Limestone, but not 



fragments, with cha- in the Paradoxides Beds. 

 racteristic tuberculate 

 surface. 



The fauna seems to indicate the incoming of a change from 

 Lower to Middle Cambrian. On balance it must be classed with 

 the Lower Cambrian, and the physical evidence points in the same 

 direction. 1 



Note. — A collection made by Mr. J. Rhodes in 1892, at Neve's Castle in 

 the Wrekin district, for the Geological Survey, contains a number of speci- 

 mens of a black rock having the lithological characteristics of the Lap- 

 worthella Limestone, and yielding Acrothyra cf. sera, Lapworthella nigra., and 

 Hyolithellus micans in similar abundance. The Paradoxides and Olenellns 

 faunas are known to be in juxtaposition in this area ; but the section at the 

 junction is not open, and it is consequently impossible to say whether the 

 Lapivorthella Limestone of Neve's Castle stands in the same relation to the 

 other beds as it does at Comley. 



Middle Cambrian. 

 Horizon Ba r Paracloxicles-groomi Grits. 



Acrothyra comleyensis. 

 Hyolithellus micans. 

 Hyolithellus micans var. robustus. 

 Helcionella obloiiga. 



Conocoryphe emarginata var. 



longifrons. 

 Dorypyge lalcei. 

 Paradoxides groomi. 

 Paradoxides spp. indet., 3 species. 



The deposits grouped in this horizon consist of three lithological divi- 

 sions : — (A) An impersistent layer of phosphatic gritty material which 

 adheres to the surface of the Lapivorthella Limestone, and is rarely more 

 than 1 inch thick ; (2) a conglomeratic deposit containing numerous blocks 

 of pre-existing limestone and clots of contemporaneous calcareous material ; 

 (3) a coarse grit, with a few similar calcareous clots and blocks of pre- 

 existing limestone. 



Horizon Ba 2 . 



Obolus sp. indet. a. I Hyolithellus micans. 



Acrotreta sp. indet. b. 



The paucity of this fauna is attributed to the crushing of the shale-beds 

 and the absence of good exposures. 



Cobbold, 1916, pp. 119, 120. 



