106 A. E. Trueman — TJie Lias of South Lincolnshire. 



The Transition Bed [acutum sub-zone), which has not previously 

 been definitely proved except in Leicestershire, Nortliamplonshire, 

 and Warwickshire, is well developed in the Lincoln district. The 

 lithology of the lower part varies remarkably, consisting of clay at 

 Bracebridge and of sand a few miles away, at the Albion works. 

 The upper part, however, in both sections, consists of green shale. 

 Dactyloids are common, throughout {Daetylioceras athUticiim, D. cf. 

 semicelatuni, D. cf. tenuicostatimi), but the zonal fossil T. acutum 

 appears to be confined to the green shale at the top. The Transition 

 Bed of this district is thus different from that of the Midlands, where 

 Dactyloids and Tiltoniceras acutum appear together in the lowest bed. 

 Thus we must either conclude that only the upper portion of the 

 Transition Bed of Lincoln is homotaxial with the Transition Bed of 

 the Midlands, or else that T. acutum did not arrive in the Lincoln 

 area until later. No indications of a break in sequence are to be 

 found either at the top or bottom of the Transition Bed. If a break 

 occurred, however, it would possibly be at the base of the green 

 shale. 



Immediately overlying the green shales of the Transition Bed at 

 Bracebridge is an irapersistent dark-grey limestone containing 

 Posidonomya hronni, succeeded by paper shales with impressions of 

 compressed ammonites. In places where the limestone is not present 

 there is a more gradual transition between the shales and the 

 junction is less easy to define. 



In the cliff above the Albion Brick Pit the Upper Lias clays were 

 formerly worked in Swan's Pit. This pit is now disused and the 

 section cannot be fully studied, but is probably as follows : — 



Cliff above the Albion Beick Pit. 



ft. in. 

 Oolitic limestone (Lincolnshire Limestone) . .80 

 Northampton Sands (ferruginous) . . . .46 



[Yeovihan and part of Whitbian deposits missing — non-sequence.] 

 suhcarinatuvi Well-laminated shales, blue and black, with ferru- 



sub-zone. ginous nodules. Fossils rare. Hildoceras bifrons. 40 



50 ft. Shell bed. Trigonia pulchella, Nucula hammeri, 



Hildoceras, Dactylioceras . . . . ..14 



Shales and shell beds with Dactylioceras. Frechiella 



subcarinata . . . . . . .88 



pseudovatum- Shell bed with Lucina 16 



falciferum Shale with shell beds and septaria containing 

 sub-zones. Harpoceras aff. mulgravitmi, Phylloceras cf. 



20 ft. 6 in. lieteropliyllum, Nucida, Belemnites subtenuis sJoovii 19 



exaratuvi Shales, not now exposed .... about 15 



sub-zone. 

 ienuicostatum Paper shales . ' . . . . . about 15 



sub-zone. 



In constructing the above section use has been made of those given 

 by Messrs. W. D. Carri and W. H. Dalton." 



The upper part of the Lias here is not very fosslliferous, but as no 

 fossils of a higher horizon than Hildoceras bifrons\\Q.xe been found, it 

 is probable that there is a non-sequence between the Lias and Oolites, 



1 W. D. Carr, Geol. Mag., Dec. II, Vol. X, p. 164, 1883. 

 " W. H. Dalton, Lincoln (Mem. Geol. Surv.), 1881, p. 33. 



