G. K. Gilbert—Origin of Jointed Structure. 47 
value of s. But this equation gives on integration an equation 
of the form, 
/s—L=C—AT. 
According to this equation the horse would absolutely reach 
the limiting speed in a finite time x Practically this may be 
true, as is in fact shown by my own equation (4) in the July 
number, so that some such equation might really represent the 
results sufficiently for all practical purposes. But the relation 
18 not a rational one, since it cannot be supposed that the horse 
will really attain his limiting speed in a finite time. After he 
had come within a thousandth of a second, it would take a 
mighty effort, and a great interval of time to compass the next 
millionth of a second. 
Moreover this equation will not hold after the limiting space 
shall have been attained, since it is the equation of a parobola, 
and the value of s will then begin to increase, which is evi- 
dently absurd. ; 
Washington University, Nov. 10, 1883. 
Arr. X.—On the Origin of Jointed Structure; by G. K. GILBERT. 
may produce incipient slaty cleavage along certain lines per- 
haps determined by crystalline structure, and that the vertical 
Mr. Walling and Mr. Crosby independently propose the the- 
pe : y independently propose 
ory that jointed structure is produced by earthquakes. Mr. 
