454 TRANSACTIONS OF SECTION C. 
importance of these interesting organisms and, with the notable exception of 
Sir Archibald Geikie’s text-book, we find but scant allusion in English geological 
works of reference to the important part played by Calcareous Alge in the 
formation of limestone deposits.* 
From the more strictly botanical standpoint, however, we are indebted to 
Professor Seward for an admirable account of the forms recognised as belonging 
to this group up to the date of the publication of his text-book on Fossil Plants 
in 1898; while in an article in Science Progress in 1894, he has also dealt with 
their importance from a geological point of view. 
Since these publications, not only have several new and important genera 
been discovered in this country and abroad, but the forms previously known 
have also been found to have a very much wider geological and geographical 
range than was formerly suspected; and I venture to hope that a summary of 
our knowledge of the part which they play as rock builders more especially in 
British Paleozoic deposits, will serve to stimulate an interest in these somewhat 
neglected organisms among geological workers in this country. 
Previous to 1894, in which year Dr. Brown first referred Solenopora to the 
Nullipores, we meet with little, if any, reference to the occurrence of fossil 
Calcareous Alge in British deposits. ; 
Indeed, in this country the subject has attracted but few workers, and they 
can almost be counted on the fingers of one hand. When we have mentioned 
the late Professor H. A. Nicholson and Mr. Etheridge, jun., Mr. E. Wethered, 
Dr. Brown, Dr. Hinde, and Professor Seward, we have practically exhausted 
the list of those who have contributed to our knowledge of the subject. To 
these we may add the name of Mrs. Robert Gray, whose magnificent collection 
of fossils from the Ordovician rocks of the Girvan district has always been 
freely placed at the disposal of geological workers, and has furnished numerous 
examples of these organisms to Professor Nicholson and the officers of the 
Geological Survey. 
It was Nicholson and Wethered who first recognised the important part 
played in the formation of limestones, by certain organisms, which, though 
referred at the time to the animal kingdom, are now generally considered to 
represent the remains of Calcareous Alge. 
The presence of these organisms in a fossil state, especially in the older 
geological formations, has only been recognised in comparatively recent years; 
though it was suggested as long ago as 1844 by Forchhammer ? that fucoids, by 
abstracting lime from sea water, probably contributed to the formation of 
Paleozoic deposits. When we remember that it was not until the researches 
of Phillipi were published in 1837 that certain calcareous deposits were dis- 
covered to be directly due to the growth of living forms of lime-secreting alge, 
it is not surprising that, only in comparatively recent years, has the importance 
of the fossil forms as rock-builders in past geological formations been recognised. 
The original genera established by Phillipi—namely, Lithothamnion and 
Lithophyllum—are now known to have a wide distribution in the present seas, 
and it is therefore natural that it should be examples of these genera which were 
the first to be recognised in a fossil state in Tertiary and, subsequently in Upper 
Cretaceous rocks. 
Thus in 1858, Professor Unger of Vienna showed the important part played 
by Lithothamnion in the constitution of the Leithakalk of the Vienna Basin, 
while seven years later, Rosanoff contributed further to our knowledge of Ter- 
tiary forms. In 1871 Gimbel published his monograph on the ‘so-called 
Nullipores found in limestone rocks,’ with special reference to the Litho- 
amnion deposits of the Danian or Maestricht beds. Since then Zithothamnion 
has also been reported from Jurassic rocks, and even from beds of Triassic age, 
though in the latter case, at all events, the reference to this genus appears to 
require confirmation. In this country the recognition of fossil Calcareous Algz 
dates from a considerably later period. It will be best first to review the chief 
genera which appear to be referable to the Calcareous Alge, and afterwards to 
discuss the part they play as rock-builders in the different geological formations. 
1 Geikie, T'eaxt-book of Geology, 4th ed., vol. i., pp. 605 and 611. 1903. 
2 British Association Report, 1844, p. 155. 
