84(1 The American Geologist. November, 1893 
CORRESPONDENCE. 
The Reproduction of Arms in Crinoids. In the cabinet of Dr. 
Welch at Wilmington, Ohio, the son of Dr. L. B. Welch, who furnished 
so many specimens to U. P. James, of Cincinnati, and other paleontol- 
ogists, there is a small crinoid considered by him to be 
Dendrocrinus casii Meek. It is interesting, however, as 
being one of two specimens of this species found by the 
elder Dr. Welch, illustrating the power of crinoids to re- 
produce their arms. The figure drawn from the original 
fragmentary specimen is sufficiently explanatory. The 
power of star-fish to reproduce their arms is often seen in 
the living specimens of the seashore. But few persons have access to 
living crinoids, and their studies in this direction must be made upon 
fossil forms, as in the present case. Aug. F. Foekste. 
Additional, Models at the Fair. — Will you allow me to call the at- 
tention of your readers to two models in the Columbian Exposition, not 
mentioned in your reference to this subject in the October Geologist. 
The first of these is a model of part of the valley of the upper Moselle, 
in the exhibit of the geographical service of the French army; on the 
same scale, horizontal and vertical (1:20,000 I thinkj, executed with 
extreme nicety, and to my eye the finest geographical model in the fair. 
It is ideal in accuracy and delicacy; far above any products of our 
American studios. 
The second is the great model of California, in the California State 
building, made by Mr. W. D. Johnson, topographer of the U. S. Geo- 
logical Survey, lately engaged in work in California. Being of a 
large area, it is somewhat exaggerated vertically; but not so much as to 
give bad impressions of form. It is tinted to give the natural colors of 
the landscape, subdued by atmospheric effect, as if viewed from a great 
altitude. Its execution is remarkably successful; and of this rather 
than of the vertically exaggerated model of New York I should say it 
"leaves little to be desired." The New York model is so violent in its 
relief, that erroneous ideas must be trained from it. 
While your article was professedly upon "Geological Maps," it nat- 
urally touched upon geographical models as well; but in omitting men 
tion of the French model and of Johnson's California, the best models 
of the exhibition were neglected, and undue prominence given to infe- 
rior work. YV. M. Davis. 
Cambridge, Mass., Oct. 14, 1893. 
The St. John Group. May I ask your attention to one or two points 
in your notice in the Sept. number of the Geologist of my article, No. 
VII. on the St. John group. 
As originally used this name was given to a series of sandstones, 
slates and shales, whose age was not definitely known by included fos- 
