SEPTEMBER 25, 1913] 
NATURE 
description of this genus from the Carboniferous rocks 
of Belgium, Giirich refers it provisionally to the Pro- 
tozoa, while Rothpletz in his description of the two 
species S. balticum and S. Holmi from the Gotlandian 
of Gotland, although admitting the difficulties of 
assigning it to any group of the animal kingdom, 
decides in favour ot its hydrozoan affinities. 
As will be pointed out later, there appears to be no 
good reason why Spongiostroma may not be indirectly 
the result of algal growths; but whatever may be the 
final position assigned to it, there can be no doubt as 
to its importance as a rock-building form in the Iliona 
limestone of Gotland. The wide extent of this 
alge horizon in the Upper Silurian of the 
Baltic area is shown by the abundance of boulders 
of these rocks scattered over Schleswig-Holstein, 
and it is probable that a careful examination will 
show the presence of this facies in the Silurian to 
the east of the Baltic provinces. 
We may conclude, therefore, that the development 
of the Spherocodium beds of Gotland probably occupy 
as wide an extension in the Baltic area as that of the 
Rhabdoporella limestones in the Ordovician period. 
With regard to other occurrences in Silurian rocks, 
it will be sufficient to note that of Girvanella in the‘ 
Silurian limestones of Queensland, Australia, recorded 
by Mr. G. W. Card in 1900, and more recently by Mr. 
Chapman from Victoria.*® 
Quite recently Mr. R. Etheridge, jun., of Sydney,’® 
has described ‘‘an organism allied to Mitcheldeania 
from the Upper Silurian rocks of New South Wales ”’; 
the figures given, however, and the description are 
not convincing that his identification can be accepted. 
The size of the tubes, which are from five to six times 
that of the largest tubes of M. gregaria, alone would 
appear to separate this organism from Mr. Wethered’s 
genus, and almost certainly from the calcareous alge. 
DEVONIAN. 
So far as I am aware, there is only one recorded 
occurrence of calcareous alge in the Devonian rocks 
of Britain—namely, in the Hope’s Nose limestone, 
from which Mr. Wethered has described aggregations 
of tubules resembling Girvanella, but in a very poor 
state of preservation. It is hoped that this meagre list 
will be increased in the near future. 
Foreign Devonian. 
On the Continent the records are, so tar, equally 
poor. At the same time, the cursory examination 
which I was able to make of the thin sections of the 
Devonian limestones exhibited in the Brussels Museum 
leads me to expect that a careful investigation of the 
Belgian Devonian limestones will yield other examples 
besides Spongiostroma. 
CARBONIFEROUS. 
We now reach the period in Paleozoic times when 
calcareous algz attained their maximum development 
‘in England, a development rivalling that which ob- 
tained in the Ordovician rocks of Scotland and the 
Gotlandian of Scandinavia. The genera here repre- 
sented include Girvanella, Solenopora, and Mitchel- 
deania. In addition to these, there occur several lime- 
secreting organisms which, though still undescribed, 
will, I think, ultimately come to be included among 
the calcareous algz. The most interesting of these 
organisms I have recently figured from the Lower 
Carboniferous rocks of Westmorland, where it forms 
a definite zonal horizon or ‘‘ band.” *° For this form, 
on account of its stratigraphical importance and for 
18 Rep. Austr. Assn. Adv. Sci.. 1907-8. 
9 Rec. Geol. Surv. N. S. Wales, vol. viii, pt. iv., 1909, p. 308, pl. 47- 
20 Q.J.G.S., 1912, vol. Ixviii. pl. 67, fig. 2. ee 
NO. 229I, VOL. 92] 
117 
| facility of reference, 1 propose the generic name of 
Ortonella.** 
Again, at the same horizon in the North-west Pro- 
vince I have frequently noticed concretionary deposits 
of limestone which occur as finely laminated masses 
often lying parallel to the general direction of the 
bedding planes, which, on microscopic examination, 
show no definite or regular structure, but have every 
appearance of being of organic origin. Many of these 
puzzling forms resemble very closely the somewhat 
obscure structures found in the Visean limestones of 
the Namur basin in Belgium, of which beautiful thin 
sections are displayed in the Natural History Museum 
at Brussels,?*, and which Giirich has described and 
figured under various names—namely, Spongiostroma, 
Malacostroma, &c., and included under a new family 
the Spongiostromidz,** and a new order, the Spongio- 
stromacee. He gives the following definition of the 
family: ‘‘Organismes marins, incrustants, coloniaux, 
A structure stratifiée. La structure de la colonie est 
indiquée, a 1’état fossile, par la disposition de petits 
grains opaques (granulations), entre lesquels il y a 
des interstices, tant6t plus étroits, tantét plus larges 
—canaux du tissu et canaux coloniaux—donnant 
naissance a un tissu spongieux. Dans _ plusieurs 
formes, on a observé des Stercomes,”’ and suggests that 
they may possibly have been encrusting foraminifera. 
I must confess that neither in the original sections 
nor in the beautiful illustrations which accompany 
his work can I see any grounds for referring these 
structures to the protozoa. 
As regards the British specimens, I have long 
regarded them as due, directly or indirectly, to the 
work of calcareous algz, on account of their intimate 
association with well-developed examples of these 
organisms, and, secondly, on account of the entire 
absence of foraminifera and other detrital organisms 
wherever this structure occurs. As, however, I have 
little doubt that they are closely connected in their 
mode of origin with the Belgian specimens, we may 
conveniently speak of them under the general term 
Spongiostroma. 
Some of the best examples known to me occur 
associated with Ortonella in the ‘ Productus globosus 
band” near the summit of the “Athyris glabristria 
zone”’ in the Shap district. They occur here in con- 
siderable 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 Giirich in plates xvii. and xx. (23). Others 
approach closely to the same author’s figures of 
Spongiostroma, Aphrostroma, &c. 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 hori- 
zons in the Lower Carboniferous of the north of Eng- 
land, 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 
21 From Orton, a village between Shap and Ravenstonedale, where this 
organism occurs in great ahundanc-. 
22 One of these is also exhibited at the Jermyn Street Museum. 
23 “Mem. du Musée Roy. d’Hist. Nat. de Belgique,” ili, 1906. 
