LOWER LIAS: CI1AUMOUTH. (Jo 
The Lias of Black Ven is exposed in three terraces that form 
the lower portions of the cliff beneath the Cretaceous rocks. The 
uppermost of these is formed for the most part of pale grey marls, 
known as the "Belenmite Beds (to be described further on). 
The terraces below are formed by the much darker shales, clays, 
and marls, which will now be noted in detail. 
Near the lop of the lowest terrace there is a prominent band of 
nodular limestone or cement-stone inclined towards the Char- 
mouth valley and terminating in the low cliff near the Coast 
Guard Station. It is slightly faulted at one point under Black 
Yen with a downthrow of 5 or 10 feet on the west. (See Fig. 
41, p. 53.) It is not however shown in the cliffs east of Char- 
mouth, as a more important fault traversing the valley, throws 
down the beds about 50 feet on the east. This fault was noticed 
by Mr. Day. 
The band of cement-stones or " Firestone Nodules "* is known 
as the Birchii Bed," from the occurrence of Ammonites Birchii. 
The specimens are known to collectors as the " Tortoise 
Ammonites," and also as " White Ammonites " from the white 
calc-spar that often fills the chambers of the shells. In the same 
nodules many small and juvenile Ammonites occur. The band 
was most accessible in the western part of Black Ven towards the 
Church Clifts ; it sometimes includes two layers of cement-stone 
nodules. 
Specimens of limestone, crowded with small ammonites {A. 
obtusus, A. plunicosta, and A. Smitlii) occur at a higher horizon 
beneath the Pentacrinite Bed ; these are often to be picked up on 
the beach, and they present resemblances to the famous Ammonite 
Marble of Marston Magna, which is on the same geological 
horizon. 
Nodular limestone with Ammonites semicostaius is said to occur 
in the shales beneath the " Birchii Bed " ; and this is not inconsis- 
tent with evidence obtained elsewhere, where this species ranges 
above the strata allotted to it as a zone. 
Fine specimens of Ammonites obtusus occur here and there in 
the clays and nodular limestones between the Table Ledge and 
the Coin Stone Bed ; this division was regarded by Dr. Wright 
as the zone of A. obtusus; here also, and more especially in the 
shaly marls above the Birchii Bed, occurs A. Brookei. Specimens 
enveloped in iron-pyrites are not uncommon. A. Bonnardi has 
also been recorded from this series. 
Above the shaly marl with A. Brookei, there are two layers 
known as the "' Two Cement Beds," which are seen in the lower 
part of the middle day-terrace of Black Ven ; and the higher 
band, which is the more conspicuous one, re-appears in the lower 
part of the cliff east of Charmouth. Tumbled masses of these 
beds have been used for paving-stone or pitching. 
Not far below the Coin Stone Bed is the layer known as the 
Pentacrinite Bed, which has yielded many fine specimens of 
* I have been informed tliat some of the nodules were formerly usod for fires, as 
fire-balls. 
