90 



THE LIAS AMMONITES. 



III. Grey marls with the green Ammonite nodules are estimated at one hundred 

 feet in thickness, and are overlain by what is locally called " The Three Tiers," con- 

 sisting of three beds of hard micaceous sandstone, interstratified with sandy micaceous 

 shale and greyish marls. These beds contain few fossils. The bones of Saurians are 

 sometimes found in the rock beds, together with impressions of Phylloceras Loscombi 

 and Lytoceras fimhriatum. Over "The Three Tiers" are about 160 feet of grey 

 micaceous marls. Two or three thin bands of mudstone and occasional nodules 

 occur in the lower part of the mass, and at rather more than 100 feet above "The Three 

 Tiers " a thicker band, containing shells and calcareous concretions, stands out from 

 the face of the cliff. Underneath this thick band is a curious and persistent layer of 

 small nodules containing chiefly fragments of Ammonites. 



The mass of grey marls terminates with a layer made up of shells and fragments of 

 Pentacrinites, and this is immediately overlain by a bed of large sandstones, from 

 4 to 6 feet in thickness, belonging to the zone of Amaltlieus margaritatus. 



Bobin Hood's Bay. — The north cheek of this bay presents a fine exposure of the 

 Henleyi-heA?,, consisting of hard marly shales interstratified with oyster-bands, forming 

 strong rock beds, having a thickness of 60 feet, with blue sandy shales, becoming more 

 argillaceous towards the base with fossiliferous nodules containing Aey. Henleyi and 

 Lytoceras Jlmbriatum. Messrs. Tate and Blake^ have carefully measured these beds and 

 drawn up the following section : 



HENLEYi-iec/s, North Cheek, Bobin Hood's Bay. 

 Base of the Maryaritatus-beds. 



10 



Series of thin oyster bands with ripple- 

 marked sandstone between 



Hard speckled shales 



White hardened band, conspicuous at 

 Castle Chamber 



Brown speckly shales 



Sandy laminated rock oysters, at base 

 10—12 in 



Brown speckly shales 



Line of ironstone doggers 



Brown speckly shales 



Sandy variable bands, occasional patches 

 of oysters 



Brown speckly shales with large 

 doggers irregularly scattered 



Thin laminated shale 



Thick- 

 ness. 



ft. in. 



4 5 



6 

 8 6 



10 



1 4 

 4 



7 4 



10 



3 6 



1 8 



Organic Remains. 



Gryphcsa cymbium, var. depressa. 



Wood. 



Gryphcea cymbium, var. depressa. 



Aeg. Henleyi. 

 Aeg. Henleyi. 



Gryphcea cymbium, var. depressa. 



'The Yorkshire Lias,' p. 91. 



