130 The American Geologist. August, 1903. 
The ultimate limits have therefore not yel been reached, not has the 
[ce ago entirely departed from the earth. marsden manson. 
San Francisco, CaL, June 24, 190,3. 
Coiumbian University Geological Department. The eastern 
branch of the summer field work in geology was conducted this year 
at Larrabee's point, Vermont, during the first week in June. Thirty 
students were present. The work was under the guidance of professor 
J. F. Kemp and professor A. W. Grabau, assisted by Mr. H. W. Shini- 
er. The Ticonderoga sheet of the U. S. G. S. was used as a basis of 
work. This section was chosen because it united so well excellent 
stratigraphic, structural, physiographic and glacial feature- ; and a 
range of rocks extending from the Archaean through the Utica. 
The Archaean and Algonkian rocks are very well developed on the 
western side of lake Champlain, as are also many igneous rocks of 
doubtful age. One of the most noticeable of the Algonkian beds is a 
very coarsely crystalline marble occurring in scattered areas over most 
of the western half of the sheet. This area was evidently above the 
sea during the Lower and Middle Cambrian time for the Potsdam was 
deposited upon its flanks in a sea encroaching from the east. But we 
find in the southeastern portion of the sheet, west of Choate pond and 
adjoining sections, Greenwich slates which Dale has correlated with the 
Georgian (Lower Cambrian). We, however, could find no definite 
traces of fossils as the cleavage runs at a high angle across the bedding. 
The Potsdam is usually a dense, gray quartzyte, becoming in places 
slightly conglomerate as it approaches the old land. 
The Ordovician series rests conformably upon the Cambrian except 
where by faulting or folding its original relations have been disturbed, 
as northeast of Sisson hill and in many other places, for the entire re 
gion is much faulted. The lowest of the Ordovician series, the Beek- 
mantown, is over this area very thick, reaching perhaps a maximum 
of eighteen hundred feet. The lowest part of this bed has many quartz- 
yte layers identified in appearance with those of the Potsdam but sep- 
arated from the latter by calcareous beds ; hence the Beekmantown. 
an areno-calcareous formation, and which represents the transition from 
the pure arenaceous beds of the Potsdam to the pure calcareous beds of 
the chazy shows here an alteration of Potsdam and Beekmantown con- 
dition-. Most of the Beekmantown is unfossiliferous, but some of the 
middle and upper beds are very full of fossils. There are several spec- 
ie- of Ophileta, including O. cotnplanata; also several species of trilo- 
bites. Most of the Beekmantown is rather heavy-bedded but in some 
places it is quite shaly. 
Upon the Beekmantown rests the chazy, a dark, heavy-bedded lime- 
stone forty to fifty feet thick. This contains many fossils, the most 
characteristic of which is Maclurea magna. The rock also contains 
very many Orthoceras and Cystoceras shells. 
The next higher formation here is the Trenton, a limestone varying 
in thickness from one hundred and fifty to two hundred feet. The 
Lowville and Black river were not here determined; but their time- 
