188 RICHARDSON : THE LOWER OOLITIC ROCKS OF YORKSHIRE. 
consists mainly of clay, the latter comprises sandstones, shales 
and impure limestones. But whilst this is the rule, here and 
there other beds come in between the Upper Lias clays and the un- 
doubted Estuarine sandstones and shales, which — on account of 
their transitional nature both as regards lithic structure and (to 
a less extent) contained fossils — render it very difficult at first 
sight to say precisely where the Lias ends and the Lower Oolites 
begin. This is more particularly the case if the palaeontological, 
and especially the ammonite evidence is ignored. 
It so happens that at the localit}^ in Yorkshire where the 
junction of the Lias and Oolites is most convenient^ studied, 
namely, at Blea Wyke, there is also the best development 
of these intervening " Transition Beds " or " Blea- Wyke Beds " 
as they have come to be called. The following record wdll give an 
idea of their nature and date : — 
Table II. — Section of the Blea- Wyke Beds, etc., 
AT Blea Wyke, Ravenscar, 
Thickness in 
Feet. Ins. 
Aaleniari / I. Sandstone, ferruginous, with scattered 
{murchisonce | pebbles .. .. .. .. ..100 
to ? scissi). I II. NerincBa-Bed : numerous gastropods 
I and lamellibranchs : 1 foot to 1 6 
{No evidence of deposits of opal- 
iniformis, aalensis and moorei 
hemerce) 
III. Sandstone, greenish-yellow with bands 
of pebbles 25 0 
IV. Brown shaly bed . . . . . . 10 
V. Sanditone, brown, full of specimens of 
Terebratula trilineata auctt. ; 
Trigonia rmnsayi Wr., Gresslya 
abducta (Phil.) 2 0 
^ (a) Sandstone, yellow, with a band of 
belemnites and pebbles at the base 1 0 
(6) Sandstone, yellow, ferruginous . . 2 0 
(c) Sandstone, soft, yellow, shaly, very 
conspicuous . . . . . . . . 10 
{d) Sandstone, soft, yellow, ferruginous, 
with irony knobs and concretions : 
in the lower part are numerous 
VI. \ specimens of Pteria with Serpula, 
Rhynchonella cynocephala auctt, etc. 20 0 
(e) Soft rotten band with blue shaly clay 
and large lump-like masses of sand- 
stone . . . . . . . . 10 
From Bed VI. have been obtained specimens 
of Dumortieria externicostata Branco, D. afi. mulW- 
costata S. Buckman, Polyplectus cf. pietralatae (Parish 
and Viale) and Pscudolioccras cf. quadrattnn S. Buck- 
Lman. 
