118 
NATURE 
[SEPTEMBER 25, 1913 
rocks was first suggested by the late Prof. Nichol- 
son,** 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 Gir- 
vanella.””. This prophecy has turned out to be fully 
justified not only as regards the north of England, 
but also in the case of other Lower Carboniferous 
districts. In 1890 Mr. E. ‘Wethered described ** two 
new forms from the Lower Carboniferous of the Avon 
Gorge and Tortworth, viz., G. incrustans, with tubes 
having a diameter of o'1 mm., and G. Ducii with a 
diameter of o'o2 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 lime- 
stone 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 neigh- 
bourhood of Ford, near the Scottish border, south- 
wards 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 3000 square miles. 
The Girvanella tubes found associated with these 
nodules usually occur in two distinct sizes having 
diameters of o'03 and o’or mm. respectively. The 
two forms are closely associated, but the finer tubes 
occur in greater abundance, 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 develop- 
ment 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 con- 
siderable area. 
Solenopora. 
The discovery of a specimen of this genus in the 
Lower Carboniferous rocks of Westmorland is of 
considerable interest, as its occurrence here gives us 
some insight into the history of its wanderings 
between the time when we last recorded it in the 
Gothlandian rocks of the Baltic area, and its re- 
appearance in the Lower Oolite of Gloucestershire. 
Whether it lived in the Baltic area during the 
Devonian and Carboniferous periods is, however, still 
unknown. The fact of its occurrence in the Caradoc, 
Carboniferous, and Jurassic rocks of the British Isles 
would appear to point to its existence not far off 
during the intervening periods, and I have hopes 
that before long it may be found in the Silurian, and 
possibly also in the Devonian rocks of this country. 
In Westmorland and Lancashire Solenopora occurs 
in considerable abundance near the local base of the 
Lower Carboniferous rocks, and contributes largely 
to the formation of limestone deposits. It is present 
wherever the lowest beds of the succession are ex- 
24 Op. cit. p. 24. 
25 O. J. G. S.; vol. 47, p- 280, pl. 11, figs. rand 2. 1890. 
NO. 2291, VOL. 92] 
posed, as at Shap, Ravenstonedale, and Meathop, 
and must formerly have flourished over a consider- 
able area. 
Though bearing a general resemblance, both in hand 
specimens and microscopic structure to the Ordovician 
and Jurassic forms, it has recently been shown by 
Dr. G. J. Hinde to be specifically distinct.** It occurs 
as small, spheroidal nodules up to an inch in 
diameter, having a markedly lobulate outline em- 
bedded in compact and usually dolomitic limestones, 
and it is occasionally associated with oolitic struc- 
ture. When fractured, it exhibits the compact por- 
cellanous texture and pale brownish tint characteristic 
of specimens of the genus found at other horizons; 
while weathered surfaces frequently show a con- 
centric and occasionally a radially fibrous. structure- 
It is noteworthy that the thallus of this organism 
shows no trace of dolomitisation, even when em- 
bedded in limestone containing over 30 per cent. of 
MgCO,. The profusion of this form in Westmorland 
would lead one to expect its occurrence in other dis- 
tricts where the lowest Carboniferous zones are 
developed; but so far as I am aware, no such 
occurrence has yet been recorded. It may be of 
interest, therefore, to mention here that a few years 
ago my friend, Mr. P. de G. Benson, brought me a 
specimen of rock from near the base of the succes- 
sion in the Avon Gorge, which on cutting I found to 
contain several examples of Solenopora identical with 
the Westmorland form. It is probable, therefore, 
that a careful microscopic examination of the lower 
horizons of the Carboniferous rocks of the scuth-west 
province will lead to the discovery of other examples 
of this interesting genus. 
Mitcheldeania, 
The specimens of Mitcheldeania  Nicholsont 
originally described by Mr. ‘Wethered were ob- 
tained from Wadley’s Quarry, near Drybrook, 
Mitcheldean, from the lower limestone shales at the 
base of the succession. Prof. Sibly, who has recently 
made a careful study of the Lower Carboniferous 
succession in the Forest of Dean,?* has traced this 
algal layer over a considerable area, and considers 
it to represent a horizon near the top of K.I. of the 
Bristol sequence. He has also noted examples of 
Mitcheldeania at a higher level, namely, in the White- 
head limestone, an horizon corresponding probably to 
the base of C2. During a recent visit to the Mitchel- 
dean district I collected specimens from both the 
lower shales, and also from the Whitehead limestone, 
and, thanks to Prof. Sibly’s kind directions, I was 
able to see numerous sections in which he has found 
this algal development. There can be no doubt that 
Mitcheldeania is here an important rock-forming 
organism at least at two horizons in this district, 
and that it occurs over a considerable area. In the 
case of the upper horizon it frequently contributes 
largely to the rock, forming in places almost entire ~ 
layers in the Whitehead limestone. As regards the ~ 
forms met with at these two horizons, the upper form 
found in the Whitehead limestone agrees exactly in 
general characters and mode of occurrence, and also 
in detailed microscopic structure, with Nicholson’s 
species, M. gregaria, from Kershope Foot. The char- 
acter of the two sets of tubes, their size and mode of 
arrangement is identical, and it is impossible to dis- 
tinguish between sections of well-preserved specimens 
from the two localities. Unfortunately, the specimens 
from the lower shales at Mitcheldean are very badly 
preserved, but if Nicholson’s distinction between the 
two species holds, we shall have to speals of the form 
2% Geol. Mag., Dec. 5, x, 289. 1913. 
27 Geol. Mag., Dec. 5, 417- 
