PRESIDENTIAL ADDRESS. 459 
Alga referred provisionally to Solenopora. From the photographs exhibited by 
Professor David on the occasion of his address to the Geological Society 
I have little doubt that this reference is correct. 
A further occurrence of Solenopora is also reported from fragments of a lime- 
stone'breccia collected by the Southern party from the western lateral moraine 
of the same glacier. Speaking of the fauna discovered in this limestone, Prof. 
David remarks : ‘ The whole assemblage is so closely analogous with that found 
in the Lower Cambrian of South Australia as to leave no doubt as to the 
~~»~-geological age of-the limestones from which these fragments are derived.'7 This 
discovery, therefore, extends the vertical range of this widely distributed genus 
down to the oldest Paleozoic rocks. It is interesting to note that the rocks in 
which the Solenopora occurs on the Antarctic Continent contain a development of 
pisolite and oolite, and that this is also the case in the Australian equivalents. 
In 1887 and again in 1891 Bornemann described and figured species of Siphonema 
and Confervites ** from the Archaocyathus limestones of Sardinia. As regards 
the former genus, it was shown by Dr. Hinde’® to be congeneric with Girvanella 
(Nich and Eth). It is of interest, however, to note that Bornemann describes 
this form as a Calcareous Alga, and compares it with existing sub-aerial alge 
growing on the surface of limestone rocks in Switzerland. The latter is stated 
by Seward to be possibly ‘a Cambrian alga, but the figures and descriptions 
do not afford by any means convincing evidence.’ 
More recently, in 1904, Dr. T. Lorenz *° has described remains of Siphoneee 
from the Cambrian rocks of 'Tschang-duang in Northern China, for which 
he erects two new genera, Ascosoma and Mitscherlichia, placing them in a 
new family, the Ascosomacew. These alge build important beds of limestone, 
the individuals often attaining a length of 4 cm. and a thickness of 15 cm. 
In 1907 Bailey reported Girvanella associated with oolites in the lowest Cambrian 
Man-t’o beds in China. It is probable, therefore, that as our knowledge of 
these rocks is extended, Calcareous Alge will be found to play an important part 
in the Cambrian limestones of the Asiatic Continent and Australia.”* 
ORDOVICIAN. 
In the Ordovician rocks, the remains of Calcareous Algze are much more 
abundant; they are very widely distributed and for the first time they become 
important rock-builders. In Britain, the chief genera met with are Girvanella 
and Solenopora. These two organisms occur abundantly in the Scottish 
Ordovician rocks of the Girvan area, where they appear to have contributed 
largely to the limestones of the Barr Series in Llandeilo-Caradoc times. 
As already mentioned, the genotype of Girvanella—G. problematica—was 
originally described by the late Professor Nicholson and Mr. Etheridge, jun., 
from the Craighead limestone, where it occurs in great numbers at Tramitchell. 
The officers of the Geological Survey also report it from the Stinchar limestone of 
Benan Hill.” 
It occurs in the form of small rounded or irregular nodules, varying in 
diameter from less than a millimetre to more than a centimetre—many of the 
nodulés showing marked concentric structure. During a recent visit to Girvan 
I was much struck by the important part played by this organism in the forma- 
tion of these upper ‘ compact’ limestones. In Benan Burn, where these beds 
are admirably exposed, the Girvanella nodules appear conspicuously on the 
weathered surfaces, being so abundant as to constitute thick layers of limestone. 
Solenopora compacta var. Peachii, which, likewise, forms important masses 
of limestone, is found, like Girvanella problematica, most abundantly in the 
Girvan area, but at a somewhat lower horizon, namely, in the ‘nodular limestone’ 
and shales forming the lower sub-division of the Stinchar Limestone. It was 
11 Eleventh International Geol. Congress Report, 1910, p. 77%. 
18 Nova Acta Ces. Leop. Car. 1887 and 1891. 
19 Hinde, Geol. Mag., 1887, Dec. III., vol. IV., p. 226. 
20 Centralb. Min., 1904, p. 193. 
*t Chapman, Proc. Roy. Soc. Vict., 1911, p. 308. 
2 Mem. Geol. Surv. United Kingdom. The Silurian Rocks of Britain vol. I., 
Scotland, pp. 487, 494, 496, 500. 
