178 LIAS OF ENGLAND AND WALES 
semicostatus. The position of these beds was first determined by 
the Kev. J. E. Cross. 
The beds attain a thickness of from 20 to 30 feet, and consist 
of harder and softer bands of brown ferruginous limestone and 
calcareous ironstone, with occasional traces of oolitic structure. 
The following are among the fossils that have been obtained : 
# 
Ichthyosaurus communis. 
Ammonites Conybearei. 
semicostatus. 
Nautilus striatus. 
Belemnites acutus. 
Pleurotomaria anglica. 
Cardinia Listeri, var. ovalis. 
gigantea. 
Gryphaea arcuata. 
Lima gigantea. 
Hermanni. 
Modiola scalprum. 
Pecten eequalis. 
sequivalvis. 
demissus. 
textorius. 
Pholadomya arabigua. 
Spiriferina Walcotti. 
Extracrinus. 
Serpula. 
Lignite. 
The more abundant forms are Gryphcea, Cardinia, Pecten, and 
fragments of Ammonites semicostatus. 
These beds have been traced northwards to the Humber shore 
east of Whitton, and southwards to near Northorpe station. 
Where uncovered by Drift, the beds are indicated by a reddish 
soil, and they are exposed in occasional small quarries, near West 
Halton, Coleby, and Thealby, where the stone is obtained for 
road-metal. 
The beds are of variable character, and consist largely of 
ferruginous and shelly limestones, brown, grey, and greenish in 
colour, with layers of ferruginous matter and ironstone. BeJs of 
a profitable character have been worked some distance on either 
side of the Trent, Ancholrne, and Grimsby railway, near Frod- 
ingham station, on Crosby, Scunthorpe, Frodingham, and Brumby 
Warrens. 
To the south of this tract exposures are few ; ironstone has been 
observed here and there, but for the most part the beds consist of 
rubbly and ferruginous limestone with clay-bands, resembling the 
unproductive beds of the Frodingham quarries.f 
The Frodingham Ironstone is overlaid by a series of blue clays 
and shales, surmounted by a band of shelly ironstone yielding 
Pecten and other fossils, and known as the Pecten-bed. 
Mr. Ussher notes the thickness of the blue clay and shale below 
the Pecten-bed to be 90 feet south of Appleby station (as proved 
by borings), and to be about 140 feet south-west of Kirton Lindsey 
railway-station. 
The lower portion of the clay has yielded Ammonites Birchii, 
but its fossils are not sufficiently well-known. 
In the upper portion, bands of chert-nodules were noticed by the 
Kev. J. E. Cross, and among the fossils the following may be 
mentioned : 
* Geology of North Lincolnshire, pp. 21, &c. 
f See Ussher, Geol. N. Lincolnshire, pp. 21-31. 
