ON THE OLDEST KNOWN FOSSIL, ETC. 
347 
reveal a structure resembling that of other Foraminiferal forms ; as, for 
example, Calcarina and Nummulina. Dr. Dawson’s description is accom- 
panied by some remarks by Dr. Sterry Hunt on the mineralogical relations of 
the fossil (Op. cit., p. 67). He observes that, while the calcareous septa, which 
form the skeleton of the Foraminifer, in general remain unchanged, the 
sarcode has been replaced by certain silicates, which have not only filled up 
the chambers, cells, and septal orifices, but have been injected into the 
minute tubuli, which are thus perfectly preserved, as may be seen by remov- 
ing the calcareous matter by an acid. The replacing silicates are white 
pyroxene, serpentme, loganite, and pyrallolite or rensselaerite. The pyroxene 
and serpentine are often found in contact, fillin g contiguous chambers in the 
fossil, and were evidently formed in consecutive stages of a continuous 
process. In the Burgess specimens, while the sarcode is replaced by loganite, 
the calcareous skeleton, as has already been stated, has been replaced by dolo- 
mite, and the finer parts of the structure have been almost wholly obliterated. 
But in the other specimens, where the skeleton stiU preserves its calcareous 
character, -the resemblance between the mode of preservation of the ancient 
Laurentian Foraminifera and that of the allied forms in Tertiary and recent 
deposits (which, as Ehrenberg, Bailey, and Pourtales have shown, are injected 
with glauconite) is obvious. 
There are_, at least_, three 
zones of crystalline lime- 
stone in the Lower Lanren- 
tian series (see diagram, fig. 
1); the specimens from Gren- 
ville bearing organic struc- 
ture belong to the highest of 
the three ; and it remains to 
be proved whether the other 
limestones (as well as a similar 
marble in the Upper Lauren- 
tian) contain it also. The 
specimens from Burgess and 
the Grand Calumet have not 
had their places determined. 
The zone of GrenviUe limestone 
(says Logan, op. cit) is in some places 
about 1,500 feet thick ; and it appears to be divided for considerable dis- 
tances into two or three parts by very thick bands of gneiss. One of these 
occupies a position towards the lower part of the hmestone, and may have a 
volume of between 100 and 200 feet. It is at the base of the limestone that 
the fossil occurs. This part of the zone is largely composed of great and small 
irregular masses of white crystalline pyroxene, some of them twenty yards in 
length by four or five wide ; and they appear to be confusedly placed one 
above another, with many ragged insterstices and many smooth-worn, 
rounded, large and small pits and subcylmdrical cavities, some of them 
pretty deep. . . . These masses of pjwoxene may characterize a thickness 
of about 200 feet, and the interspaces among them are filled with a mix- 
Fig. 2. — Diagram of a portion of JSozoon (after 
Carpenter ). — a b c, chambers in three tiers 
communicating fay more or less constricted 
passages, or (as in a) by a passage of two 
small openings ; a a, the proper or essential 
shell, tubuliferous and thin -,bb, intermediate 
or supplementary shell ; c. Stolon-passage from 
tier to tier; d, Ramifying tubes (arising from 
a “ lacuna”) in the ‘‘ supplementary shell.” 
