344 Notes and Comments. 
studying the lithological characters of the lower carboniferous 
rocks of the North of England and the Border country, I 
have been still further impressed by the abundance of these 
nodular structures at several horizons, and the large tracts 
of country over which they extend. An examination of these 
nodules in thin sections showed their obvious organic character, 
and I was at first inclined to refer them to the stromatoporoids. 
Dr. G. J. Hinde, who was kind enough to examine my specimens 
from the Shap district, reported, however, that they were 
probably not Stromatoporoids, but calcareous alge, and 
referred me to the descriptions of Solenopora published by 
the late Professor Nicholson and Dr. Brown. Since then I 
have examined a large number of nodules collected from 
different horizons in the lower carboniferous rocks of Britain. 
and Belgium; and the examination has convinced me that 
the remains of calcareous alge play a very much more important 
part in the formation of these rocks than has hitherto been 
generally realized.’ 
CALCAREOUS ALG. 
— In conclusion Professor Garwood opined that “ The facts 
given regarding the geological distribution and mode of 
occurrence of these organisms lead us to several interesting 
conclusions. In addition to the evidence of the important 
part they play as rock-builders, it is evident that certain 
forms flourished over wide areas at the same geological periods, 
and might well be made use of in many cases with considerable 
reliability as proofs of the general contemporaneity of two: 
deposits. Thus, as general examples, we may cite the wide 
distribution of Solenopora compacta in the Baltic Provinces, 
Scotland, England, Wales, and Canada during Llandilo- 
Caradoc times. The wonderfully persistent development of 
the Rhabdoporella facies over the whole of the Baltic area at 
the close of Ordovician times was of so marked a character 
that by means of boulders scattered over the North German 
plain it can even be made use of for tracing the direction of 
flow of the ice-sheet during glacial times. Again, to take 
examples nearer home. The Ovtonella band found throughout 
Westmorland and north Lancashire near the summit of the 
Tournaisian occurs so constantly at the same horizon as to 
constitute one of the most valuable zonal indices in the suc- 
cession of the North-West Province, and can be used with 
the greatest confidence not only for correlating widely separated 
exposures, but also affords valuable evidence in the case of 
tectonic movements. Other examples are supplied by the 
“ Girvanella Nodular band”’ at the base of the upper Dibuno- 
phyllum zone, and the Muitcheldeania gregaria beds in the 
north of England and the Forest of Dean.’ 
Naturalist, 
