62 The American Geologist. January, 1903. 
CORRESPONDENCE. 
Apatite crystals, Antwerp, New York. The following is the 
analysis o.f some crystals of apatite that were obtained near Antwerp, 
Jefferson Co., New York, some time ago. They were olive green prisms 
and were about two centimetres long, and eight millimetres in di- 
ameter. The analysis was made in the chemical laboratory of Cornell 
college by assistant Frank L. Hann. 
CaO 48 . 20 
P2O5 41.00% 
Ca3(P04). 8g.20% 
SiO. 0.60 
ALOs g.oo 
CaF2 
1.20 
100.00% 
Mount ]'cnion, loii'a. Dec. 24, IQ02. Nicholas knight. 
Fall Excursions of the Geological Department, Columbia Uni- 
versity. The weekly fall excursions of the Columbia geological de- 
partmemt closed, as usual, on the last Saturday in November. These 
are usually half-day excursions and take place on Saturday forenoon. 
Local sheets of the U. S. Geological Survey, note books, hammers and 
compasses are necessary for each participant. Each excursion is guid- 
ed by at least one officer of the department. New York city, especially 
Harlem and its environs, is an ideal place for short excursions of ex- 
ceptional geological interest. The university itself is situated upon the 
area of the Manhattan schist which is believed by ttate geologist Mer- 
rill to be metamorphosed Hudson River shale. This schist is exceed- 
ingly full of pegmatyte dikes in which there is frequently a great 
abundance of tourmaline. There are also veins or interbedded strata 
which are now hornblende. These are of problematic origin. In places 
they are very numerous varying in width from a fraction of an inch to 
several feet and in length extending at times through an entire outcrop 
several hundred feet. They frequently end very abruptly. The Man- 
hattan schist is at times so full of garnets as to merit the name of gar- 
net schist- This is well shown just north of the convent of the Sacred 
Heart on 135th St. near Amsterdam Ave. There are fine examples of 
pinched folds in the Manhattan schist where folded in the more gneis- 
soid strata. The schist is frequently pinched into complete cylinders. 
These were noted and described many years ago by Prof- Dana. 
The Manhattan schist rests, apparently conformably, upon the In- 
wood lime.stone. This is a very coarsely crystalline rock which weath- 
ers into a coarse lime-sand. On account of its great solubility it usu- 
ally occupies the valleys. Prof. Hobbes has lately readvanccd an old 
theory, held by Dana and others, of the fault formation of thcsj val- 
levs. The \al1cv breaking through Morningsidc Park ridge at i2Stli 
