1887. ] NEW YORK ACADEMY OF SCIENCES. 21 
freshment of a muscle can only take place ordinarily by its re- 
laxation. Even a momentary relaxation is often sufficient; but 
without such relaxation, exhaustion of the muscle soon takes 
lace. 
; Dr. Houghton found, from numerous experiments, that the 
muscles of the human arm, extended and supporting a weight 
of two pounds held in the hand, became completely exhausted 
in four minutes. By the interlocking of the primary feathers 
of the wings of birds, the extensor muscles of their feathers are 
completely relieved, and rapid exhaustion prevented. Andif we 
consider, further, that when the body of the bird is suspended 
or hung between the extended wings, it is probable, and, in- 
deed, may be demonstrated as almost certain, that the action of 
the air pressure from beneath serves to keep the whole wing 
extended at the elbow without appreciable muscular effort ; the 
only effort in soaring is thus merely that which gives the slight 
movements to the tail and wings by which the body is guided 
or steered with or against the air currents. 
The PRESIDENT spoke upon the problem of the soaring of 
birds, and favorably commented upon the discovery claimed by 
Prof. Trowbridge. 
Capt. A. W. VocpEs exhibited an album of Alg@, once the 
property of Prof. Harvey, which were the types of the descrip- 
tions by that author in his ‘‘ North American Alge,” published 
by the Smithsonian Institution. 
Dr. ALEXIS A. JULIEN read a paper entitled: 
ON THE GEOLOGY AT GKEAT BARRINGTON, MASSACHUSETTS. 
An examination of the limestone belt of Western New En- 
gland, at various points, leads me to present the following views: 
First: In proof of the local existence of smaller dolomytic 
beds, distinct from the main sheet and lying at a higher hori- 
zon. 
Secondly: In explanation of the peculiar physical and min- 
eralogical characteristics of the material of these outliers, as il- 
lustrated by one in the town of Great Barrington, Massachu- 
setts. 
I. General Stratigraphy of the Stockbridge Limestone. 
Recent geological investigations have shown that this sheet of 
crystalline limestone, which, for the sake of convenient distinc- 
tion, has been called the ‘‘ Stockbridge Limestone,” extends for 
