January, 1900. 
Teller— The Hamilton Formation. 
49 
been found. On what he based his identifications it is difficult to 
say as none of the species quoted have ever been found at the 
locaHty. The Orthis and Avicula are characteristic species of the 
Tentaciilite hmestone of the water-hme group of New York, a for- 
mation that very clearly has no representation in this state. Leper- 
ditia alta is a characteristic species of the Lower Helderberg, no 
portion of which formation was then exposed at the locality, while 
Tentaculites, which is found in the water-lime group, is also a very 
common genus in the Hamilton, being fairly abundant at Hum- 
boldt in the upper layers, while in New York it forms almost a 
compact mass in some of the Hamilton shales. 
A collection of the fossils of the locality was made by Prof. T. 
C. Chamberlain, then an assistant on the survey ; these were sub- 
mitted to Prof. R. P. Whitfield, of New York, a recognized au- 
thority on such subjects, who pronounced them to be characteristic 
Hamilton forms, and that no water-lime forms were contained in 
the collection, although, as he says, ''there were among them forms 
characteristic of the corniferous," a formation lower than the 
Hamilton, yet still above the water-lime, "as well as a few forms 
which have their position defined as belonging to the Chemung," 
a still higher formation than the Hamilton. Prof. Chamberlain, 
geologist of the state, in his report, "Geology of Wisconsin," Vol. 
H., Part H., 1872, discusses very fully the Devonian Age and the 
Hamilton group, the only representative of the age in this state. 
As recognized the formation has comparatively a very limited 
geographical area, lying adjacent to Lake Michigan, immediately 
north of the city limits of Milwaukee, it has been traced for a 
distance of about six miles north along the lake shore, and extend- 
ing about the same distance into the state, it rests in part upon the 
laminated shales of the Lower Helderberg, and partly upon the 
Niagara limestones ; it has a thickness, as far as known, of about 
twenty-six feet, and dips slightly to the southeast. The most 
extensive outcrop is that at the quarries of the Milwaukee Ce- 
ment Company, where it rests upon the non-fossiliferous shales 
of the Lower Helderberg, which latter formation has no exposures 
at the locality, but forms the sole of the quarries as the cement rock 
is removed. This locality is regarded as the tvpical exposure of 
the Hamilton group in this state, and is the locality from which has 
been collected all of the type specimens of fossils, except three(i), 
that have been described from the formation in the state. Other 
exposures are found in Section ti, Town of Granville, in the rail- 
way cut immediately south of the station of Brown Deer, where 
are exposed about three feet of the formation ; this is the typical 
1. For a list of the species of tlie formation see The Fauna of the Devonian 
Formation at Milwaukee, Wis., in Jottmal of Geology, Vol. VII. No. 3, 1899. 
