MIDDLE LIAS : YEOVIL. 205 
rock at the base of the Inferior Oolite. The rock becomes more 
attenuated east of Montacute station, north-east of Preston, and near 
Brimsmoor Tree, north of Yeovil ; being reduced to 1 foot 6 inches 
or 1 foot in thickness. At Preston the rock (a hard iron-shot lime- 
stone) contains a few small pebbles of quartzite, but it is said to 
burn to a " wonderful good lime," and here as elsewhere it is used 
for road-metal. 
The Rock-bed rests on micaceous sandy loam or shales, and 
owing to its poor development it forms no prominent feature, the 
escarpment north of Yeovil being mainly formed of the under- 
lying micaceous sandy shales. It may, however, be traced south 
of Longcroft, by the lane that leads to Brimsmoor Tree. South- 
wards the ground very nearly corresponds with the dip-slope, so 
that as far as the high-road between Yeovil and Preston, the 
Rock-bed is reached in several places beneath a few feet of Upper 
Lias. (See Fig. 66.) 
It is'noteworthy that the Rock-bed, where it comes to the surface, 
is much piped or furrowed by the action of carbonated water, the 
residue being a brown ferruginous loam. In places it may be 
entirely decomposed at its outcrop ; and as the Tipper Lias base- 
ment-beds are not very thick or durable, and are overlaid by 
laminated micaceous sandy shales, resembling the beds below the 
Rock-bed, it becomes exceedingly difficult to trace a boundary 
between the Middle and Upper Lias, where there are no sections,' 
as in the tract north-east of Yeovil. This explanation probably 
accounts for the difficulties met with between Bridport and Chard. 
The pale earthy limestones of the Upper Lias rest in places 
directly on the Marlstone near Yeovil, and sometimes form one 
block, as in the coast-section at Thorncombe Beacon. The united 
thickness of these stone-beds is about 7 feet, and they have 
furnished a limited supply of water to wells in the immediate 
neighbourhood of Yeovil. (See p. 315.) 
The following species of fossils were collected by Mr. J. Rhodes 
and myself from the Marlstone near Yeovil, north-east of Preston 
and at Brimsmoor Tree ; and they were identified by Messrs. 
Sharman and Newton : 
Ammonites Engelhardti. 
margaritatus. 
spinatus. 
Belemnitea ventralis P 
Amberleya. 
Arcomya. 
Avicula inaequivalvis. 
Cardinia concinna. 
Gryphaea cymbium. 
gigantea. 
Lima punctata. 
Pecten sequivalvis. 
demissus. 
Pecten (allied to) dentatus. 
. julianus ? 
lunularis. 
Pinna Hartmanni P (cast). 
Pleuromya coatata. 
Unicardium globosum. 
Rhynchonella acuta. 
tetrahedra. 
Spiriferina rostrata. 
Terebratula subpunctata. 
Waldheimia quadrifida var. cornuta. 
resupinata. 
There is an example of Ostrea sporidla from South Petherton 
in the Woodwardian Museum at Cambridge. This fossil is more 
abundant in the Martetone of Banburv. 
