126 
Proceedings of the Royal Irish Academy. 
adopted by the two geologists of the time who have made the most 
special studies of the rocks in question, Giimhel in Germany, and 
Credner in J^orth America. 
It would be a thankless task to follow Messrs. King and Rowney 
through their long paper, which abounds in statements as unsound as 
those I have just exposed, but I cannot conclude without calling at- 
tention to one misconception of theirs as to my view of the origin of 
limestones. They quote Professor Hull's remark to the effect that 
the researches of the Canadian geologists and others have shown that 
the oldest known limestones of the world owe their origin to Eozoon, 
and remark that the existence of great limestone beds in the Eozoic 
rocks seemed to have influenced Lyell, Eamsay, and others in admitting 
the received view of Eozoon. Were there no other conceivable source 
of limestones than Eozoon or similar calcareous skeletons, one might 
suppose that the presence of such rocks in the Laurentian system 
could have thus influenced these distinguished geologists, but there 
are found beneath the Eozoon horizon two great formations of lime- 
stone in which this fossil has never been detected. When found, 
indeed, it owes its conservation in a readily recognizable form to the 
fact, that it was preserved by the introduction of serpentine at the time 
of its growth. Above the unbroken Eozoon reefs are limestones made 
up apparently of the series of Eozoon thus preserved by serpentine, 
and there is no doubt that this calcareous rhizopod, growing in water 
where serpentine was not in process of formation, might, and probably 
did, build up pure limestone beds like those formed in later times from 
the ruins of corals and crinoids. 'Not is there anything inconsistent 
in this with the assertion which Messrs. King and Rowney quote 
from me, viz., that the popular notion that all limestone formations 
owe their origin to organic life is based upon a fallacy. The idea 
that marine organisms originate the carbonate of lime of their skele- 
tons, in a manner somewhat similar to that in which plants generate 
the organic matter of theirs, appears to be commonly held among 
certain geologists. It cannot, however, be too often repeated that 
animals only appropriate the carbonate of lime which is furnished 
them by chemical reaction. Were there no animals present to make 
use of it, the carbonate of lime would accumulate in natural waters till 
these became saturated and would then be deposited in an insoluble form; 
and although thousands of feet of limestone have been formed from the 
calcareous skeletons of marine animals, it is not less true that great 
beds of ancient marble, like many modern travertines and tufas, have 
been deposited without the intervention of life, and even in waters 
from which living organisms were probably absent. To illustrate 
this with the parallel case of silicious deposits, there are great beds 
made up of silicious shields of diatoms. These during their life- 
time extracted from the waters the dissolved silica, which, but for 
their intervention, might have accumulated till it was at length de- 
posited in the form of schist or of crystalline quartz. In either case 
the function of the coral, the rhizopod, or the diatom is limited to assi- 
