LS ——<=<x<— 
PRESIDENTIAL ADDRESS. 465 
the ‘ Productus globosus band’ near the summit of the ‘ Athyris glabristria zone’ 
in the Shap district. They occur here in considerable masses, often many 
inches in thickness, and form undulating layers parallel to the bedding, and 
somewhat resembling huge ripple-marks. Thin sections show little definite 
structure, but consist of what appears to be an irregular flocculent precipitate 
of carbonate of lime, the interstices being filled with secondary calcite. Some 
of the layers resemble almost exactly, both in hand specimens and microscopic 
structure, the figures of Malacostroma concentricum given by Girich in plates 
XVII. and XX.°° Others approach closely to the same author’s figures of 
Spongiostroma, Aphrostroma, etc. In all cases they appear to be due to the 
precipitation of carbonate of lime in the neighbourhood of algal growths. I 
have also met with similar deposits, not only at other horizons in the Lower 
Carboniferous rocks of the North of England, but also in the Forest of Dean and 
in the rocks of the Avon Gorge; while quite recently Mr. C. H. Cunnington 
has sent me examples from several horizons in the Carboniferous Limestones of 
South Wales. 
Girvanella. 
This organism appears to play a considerable part in the formation of 
calcareous deposits in the Lower Carboniferous rocks of Britain. Its presence 
in these rocks was first suggested by the late Proiessor Nicholson,*! in his paper 
where he remarks: ‘I have found some of the Carboniferous Limestone of the 
North of England to contain largely an ill-preserved organism which will, I think, 
prove to be referable to Girvanella.’ This prophecy has turned out to be fully 
justified not only as regards the North of England, but also in the case of the 
Lower Carboniferous beds of other districts. In 1890 Mr. E. Wethered 
described °° two new forms of this genus from the Lower Carboniferous rocks of 
the Avon Gorge and Tortworth, viz. : G. incrustans, with ‘ubes having a diameter 
of O11 mm., and G. Ducii with a diameter of ‘(02 mm. Mr. Wethered appears to 
rely chiefly on the size of the tubes for the differentiation of these species, but 
as this distinction was made at the time when Girvanella was still considered to 
belong to the Rhizopods, and as the size of the tubes frequently varies in the 
same specimen, it is doubtful whether these species can be maintained. Mr. 
Wethered’s specimens were obtained from the limestone near where the Bridge 
Valley Road joins the river bank, apparently at the base of Dr. Vaughan’s Upper 
Dibunophyllum Zone. The position of this limestone is of interest, as it appears 
to correspond very closely with the horizon of the ‘ Girvanella Nodular Bed,’ 
which forms a well-marked band at the base of the Upper Dibunophyllum Zone 
throughout the whole of the North and North-West of England. Indeed, I have 
traced this band at intervals from the neighbourhood of Ford, near the Scottish 
Border, southwards through Northumberland and the Pennine area to Penygent, 
and from the west coast at Humphrey Head through Arnside and Shap to the east 
coast, near Dunstanburgh. These organisms must, therefore, have flourished 
over an area of at least 3,000 square miles in the North of England alone. 
The Girvanella tubes found associated with these nodules usually occur in 
two distinct sizes having diameters of ‘03 and ‘01 mm. respectively. | The 
two forms are closely associated, but the finer tubes occur in greater abund- 
ance, and are much more closely interlaced. They resemble Mr. Wethered’s 
description of the two species from Gloucestershire, and the figures he 
gives in illustration of these might serve very well to represent our northern 
forms. 
The best exposure showing the important development of these Girvanella 
nodules is to be found on the dip slopes forming the eastern shore of Humphrey 
Head in Morecambe Bay, where the base of the Upper Dibunophyllum zone 
is exposed over a considerable area. 
Solenopora. 
The discovery of this genus in the Lower Carboniferous rocks of Westmor- 
land is of considerable interest, as its occurrence here gives us some insight into 
°0 Op. cit. (2). 51 Op. cit. (4), p. 24. 
” Q.J.G.S., 1890, vol. 46, p. 280, pl. XI., figs. 1 and 2. 
1913, HH 
