142 Proceedings of the Royal Irish Academy. 
point of view before their organic origin can be admitted The 
post-Laurentian age of the Tndor limestones now appears to be esta- 
blished. Mr. H. G. Vennor, to whom is due this credit, is disposed to 
correlate them with the Potsdam group — the probable equivalent of the 
Cambrian Lingula flags ; and Dr. S. Hunt, who seems to agree with 
him, has ventured to include them in his " Terranovan Series."* Dr. 
Dawson states that they are not more metamorphosed than many of 
those which retain fossils in the Silurian system. f J^ow, Potsdam 
or primordial" fossils are «^zm^?<rm^ in some of the rocks in liew- 
foundland and ^few Brunswick, with which the Tudor limestones have 
been correlated: hence, if the creature of the dawn" lived in the 
Terranovan age, surely we have a right to expect the Tudor lime- 
ston'es — so highly promising in organic remains as they now appear to 
be from Dr. Dawson's statement (also other Terranovan deposits that 
are fossiliferous) — to afi'ord indisputable evidences of its existence, 
instead of the mere ''fragments" and other extremely doubtful 
examples they have hitherto yielded. . . . There is one point not to 
be lost sight of in connexion with the last specimens. Their presumed 
organic nature would never have been determined except by com- 
paring them with the perfect specimens of '' Eozoon" that occur in the 
'' highly crystalline'''' (Dawson) rocks of the Laurentian system ! Is not 
this cii'cumstance the very reverse of what a palaeontologist, conver- 
sant with mineralogy, can accept before he allows himself to embrace 
the various mysteries that make up the eozoonal belief ? 
7th. We objected to Dr. Dawson assuming the laminated arrange- 
ment to be typical, when, from the description of '' Eozoon," as given 
by different writers, and from our own observations, it appeared to be 
exceptional. Besides, we have nowhere ''reasoned from fragments 
confusedly intermixed," but from examples of " unbroken" acervuline 
arrangement ; which, understanding it to be the general one, we must 
still consider to be typical. The Tetradium illustration is entirely 
inappropriate. 
8th. We are not aware of having stated anything implying the 
opening sentence of this paragraph. The "chamber casts" usually 
consist of serpentine — occasionally of malacolite, and loganite ; and it 
ought to be known to Dr. Dawson that these minerals have no relation, 
as we have already pointed out, to the ordinary in-filling substance 
forming the casts of recent and fossil foraminifers : J nor do they occur 
in fossils, except, perhaps, in such as are metamorphosed. Our ex- 
perience of calcareous organisms found in limestone is, that wea- 
thering^^ developes them; the cause of which is due to their being 
usually in a different molecular condition — crystalline, or semi-crystal- 
line — to that of the rock containing them. "The fragmental speci- 
mens from Madoc," stated to be " actually wholly calcareous," also 
* " American Journal of Science," July, 1870, pp. 511, 512. 
t Nature, No. 67, p. 287. 
X " Proceedings of the Royal Irish Academy," vol. x., p. oiO, also, see Postscript. 
