.84 Calvin on the Hamilton in Ontario. 
gether with a number of other species. One of the most 
interesting corals is liic very pretty, but unfortunately rare, 
Microcyclus discus Meek and Worthen. Of this species the 
writer obtained quite a number of specimens and is able to con- 
firm Nicholson's determination of the identity of this form with 
that described by Meek and Worthen in the Geology of Illi- 
nois, vol. iii. 
Thei'e is practically nothing else but corals in the coral zone. 
Polyzoa of various genera and species are, however, not un- 
common. Dwarfed forms of Spirifera fmbriata Conrad, are 
found occasionally. About two miles southeast from Widder 
there is an outcrop of the coral zone in which N'uclcocrinus sp., 
and Pentremltes lycorias Hall, were found, but these species 
must be very rare. That most ubiquitous and usually most 
abundant of all the Hamilton species, Airypa rcticidaris Lin. 
is represented in my collections from Ontario by only two or 
three specimens, and these were found loose near the base of 
the coral-bearing beds. 
The coral bearing stratum is well developed above the beds 
containing the long-winged Spirifer at Bartlett's Mill; and along 
the river below the mills it may be seen at intervals for a num- 
ber of miles. At Rock Glen, near Arkona, it extends from the 
bottom of the gorge up almost to the summit. Near the sum- 
mit, however, the corals stop abruptly. The bluffs are crowned 
by beds of the third division, and into these beds not a single 
one of the jDrominent corals of the middle division, so far as we 
can see, was able to pass. 
The third or upper division is the one exposed in the railway 
cut near Widder. As we have said it occurs at the summit of 
the bluffs at Rock Glen. It may be seen occupying the same 
relation to the beds already described at a number of points 
between Rock Glen and Bartlett's Mills. 
In the third division we have an entirely new fauna, so far 
at least as the prominent forms are concerned. Most abundant 
of all the species is Spirifera mzicronata Conrad, but so differ- 
ent from the variety of the lower beds that, were it not for 
intermediate forms found elsewhere, we should be compelled to 
regard the varieties of the two zones as very distinct species. 
The kS". mucronata of the upper beds is a thick shell with few 
