1 82 The American Geologist. September, looi. 
the cement works quarry less than a mile east of the town,, 
near the lake shore, or approximately southeast of the preced- 
ing locality. This is desig-nated Loc. 9. 
The rock first appears on the section line, about a mile 
north of the town (Sta. 4). It appears at intervals to the north 
of this, and is prominently exposed* in the terrace whicli crosses 
the section line in a direct northeast line from the quarries. 
(Sta. 8). 
This terrace continues northwestward and furnished an- 
other good exposure of the limestone about a tenth of a mile 
west of the section along the first west road. (Stat. 9a, 
Loc. lb.) 
Loc. I. Quarries northeast of Alpena. The limestone is 
here almost wholly composed of corals and hydro-corallines,, 
though brachiopods and other organisms are not wanting. The 
corals are Favosites and Acervularia, the former probably rep- 
resented by a number of species. Large masses of the rock 
are entirely made up of these corals, which appear to be still 
in the place where they grew. Other large masses of the rock 
are composed of the hydro-coralline Stromatopora and allied 
genera, which also appear to be represented by several species. 
Among the smaller corals, species of Zaphrentis, Aulopora, and 
Ceratopora predominate, Avhile the Bryozoa are chiefly repre- 
sented by fenestelloids, and Lichenalia-like types. The chief 
brachiopods are: Atrypa reticularis, (an extremely convex 
form), Spirifer cf. .S". niiicronatiis, Stropheodonta, several spe- 
cies, Cyrtina unibonata var alpenensis, Gypidula romingeri etc. 
The central mass of limestone of this region has all the 
characteristics of an ancient coral reef in which the chief reef- 
builders were the Favosites Acervularias, and Stromatoporas. 
These formed the main mass of the reef, while between them 
grew the smaller species, and the other organisms which go to 
make up the ensemble of the reef population. A careful exam- 
ination of sections in the quarries shows that there is an ab- 
sence of stratification and regularity of structure in general, 
within the reef portion of this limestone. This is to be expect- 
ed, since this portion of the mass is entirely of organic origin. 
In form, this portion is dome-like, and the stratified beds of 
limestone which flank it, dip away from it in all directions at 
an angle exceeding that of the normal dip of the strata of this 
region. 
