CARBONIFEROUS LIMESTONE OF TYTHERINGTON DISTRICT. 101 
Seminula-Zone. 
These rocks occupy a very wide area. They underlie the 
Dibunophyllum-beds at Woodhouse Down and form the "ridge" 
till the outcrop widens at Alveston, whence they extend to 
Tockington and Olveston. They are well-exposed to the north of 
Itchington, being shifted southwards by the faults already alluded 
to. The upper beds as exposed are generally compact limestones 
with abundant Lithostrotion martini. But little is seen of rubbly 
or concretionary limestone, such as plays so prominent a part in 
the Sodbury section, though some indications of this lithological 
type occur in exposures near Alveston vicarage. As in the 
Tytherington section, there is a good development of fossiliferous 
oolite (Seminula- Oolite) in the lower part of the Upper Seminula- 
beds (S 2 ) ; this is best seen in a small quarry by the Methodist 
Chapel west of David Lane, Alveston. Another old quarry a little 
further S.W. is noticeable for a long bedding plane of dolomitzed 
limestone covered with large masses of Lithostrotion basaltiforme 
and Syringopora finely weathered out. 
There are many exposures of limestone with abundant Litho- 
strotion martini in the neighbourhood of Old Down, one being 
seen by the roadside leading up from Lower Hazel ; these are in 
the lower part of S 2 . By far the best exposure of this horizon 
occurs, however, in the Tockington hill quarry which is in active 
work. This is in massive limestone, often oolitic, with Seminula- 
bands and great masses of Lithostrotion martini and Syringopora 
exposed on the bedding planes. The lower Seminula-beds (S i ) are 
very little seen, and the most interesting point about them is the 
occurrence of a well-marked band of hard red and yellow grit 
exposed by a cottage a third of a mile south-east of Oldown 
House, and reached by a turning out of Foxholes Lane. The 
grit has been much used for building the walls here. It is also 
exposed by two cattle-ponds in the fields to the south-west of 
Upper Hazel, and much debris occurs in the fields N. of the 
Alveston road at Little Down. In the i-inch Geological Ordnance 
Survey Map this grit is coloured as Old Red Sandstone, and is 
represented as brought in by a strike fault, but there can be 
no doubt that this band is quite comparable to that occurring 
at much the same level in the Sodbury section. The Firestone- 
bands in the Tytherington quarry are at a higher horizon and are 
calcareous sandstones effervescing strongly when treated with 
hydrochloric acid. No effervescence occurs on treatment of the 
grit from near Oldown House with acid. 
Throughout all the area hitherto described, the south-easterly 
dip is maintained, but further west the strike swings round, and 
throughout the band of limestone, on which Olveston stands, there 
are numerous exposures of Seminula-beds with a south-westerly 
dip. The best exposure is at Harn Hill quarry, Elberton, where 
