Editorial' Comment. 391 
need not be thought of as proving that locahty to have been 
southward from the then equatorial Hne. Rather the turning 
is strongest in the early zoarial growth and later becomes 
confused irregularly, suggesting that the character is only a 
hereditary one; and that the species possessing it may have 
then recently immigrated from south of the equator. 
EDITORIAL COMMENT. 
Troost's Map of the environs of Philadelphia. 
In Marcou's Mapoteca Geologica Americana (Bulletin 
No. 7. U. S. Geological Survey 1884), on page 64, is given 
the following; 
1826 —Troost (Gerard). Karte der Gegend von Philadelphia. 
Accompanying 'Geological survey of the environs of Philadel- 
phia," cited by C. Gotta, in his "Geognostische Karten unseres Jahr- 
hundert's 1850, p. 48, No. 533. This map is unknown even in Phila- 
delphia, and contemporaries of Troost, such as the late T. Conrad, 
and Mr. Isaac Lea, had never heard ot such a map. It is very 
doubtful if it exists. 
In view of the above statement it may be worth while to 
call attention to the fact that a map of the above area was 
published in 1826 and issued in a pamphlet of 40 pages, en- 
titled, Geological | Surve}' | of the | Environs of Philadel- 
phia; I Performed by order of the | Philadelphia Society for 
promoting Agriculture. | By | G. Troost, M. D. | Philadel- 
phia: I Published by H. S. Tanner, 177 Chestnut Street. | 
Clark & Raser, Printers, 34 Carter's Alley. | 1826. | 
The map itself is some ten by fourteen inches, and com- 
prises that part of Pennsylvania forming a semicircle or seg- 
ment of a circle, "whereof the center is the rotunda in High 
street, Philadelphia, and the radii extend 15 miles, bounded 
on the east by the River Delaware." The rocks are all 
classed as primmdial, and as colored on the map the area 
as far north as Chestnut hill and a little be)'ond belongs to 
the gneiss formation, beyond this being narrow belts of, 
first, primitive clay-slate, and second, limestone, with a 
small area of serpentine interpolated between the gneiss 
