466 TRANSACTIONS OF SECTION C._ 
the history of its wanderings between the time when we last recorded it in 
the Gotlandian rocks of the Baltic Area, and its subsequent reappearance 
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 Carboniterous rocks, and contributes largely 
to the formation of limestone deposits. It is present wherever the lowest beds 
of the succession are exposed, as at Shap, Ravenstonedale, and Meathop, and 
must formerly have flourished over a considerable area. 
Though bearing a general resemblance, both in hand specimens and in micro- 
scopic 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 embedded in compact and usually dolomitic limestones, and it is 
occasionally associated with oolitic structure. When fractured, it exhibits 
the compact porcellanous texture and pale brownish tint, characteristic of 
specimens of the genus found at other horizons, while weathered surfaces 
frequently show a concentric and occasionally a radially fibrous structure. It 
is noteworthy that the thallus of this organism shows no trace of dolomitisation, 
even when embedded 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 districts 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 
succession 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 §.W. Province will lead to the discovery of other 
examples of this interesting genus. 
Mitcheldeania. 
The specimens of Muitcheldeania Nicholsoni originally described by Mr. 
Wethered were obtained from Wadley’s Quarry, near Drybrook, Mitchel- 
dean, from the lower limestone shales near the base of the succession. Pro- 
fessor Sibly, who has recently made a careful study of the lower Carboni- 
ferous 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 2 
of the Bristol sequence. He has also noted examples of Mitcheldeania at a 
higher level—namely, in the Whitehead limestone, an horizon corresponding 
probably to the base of O 2. During a recent visit to the Mitcheldean district 
I collected specimens from the lower shales, and also from the White- 
head Limestone, and, thanks to Professor 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. With 
regard to the forms met with at these two horizons, the upper one, found in the 
Whitehead Limestone, agrees exactly in general characters and mode of occur- 
rence, and also in its detailed microscopic structure, with Nicholson’s species, 
M. gregaria, from Kershope Foot; the character 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, 
53 Geol. Mag. 1913, Dec. V., vol. X., p. 289, pl. X. 
54 Geol. Mag., 1912, Dec. V., vol. IX., p. 417. 
