OCTOBER 29, 1897. ] 
the regret of the Section, he was unable to 
be present. 
GrorGE W. Patterson, JR. 
UNIVERSITY OF MICHIGAN. 
A NEW METHOD OF SYNCHRONIZING 
STRATA.* 
For nearly a century it has taxed strati- 
graphical geologists to the utmost to devise 
some rational and practical method by 
which the strata of the globe, the exposed 
sections of which are not visibly connected, 
can be brought into synchronous juxtapo- 
sition. Various schemes have from time 
to time been proposed, tried and aban- 
doned. While it is a simple matter to 
correlate two rock outcrops which are not 
far away from each other, the difficulties 
rapidly increase with distance and by ex- 
isting standards the determination of the 
exact equivalents finally become almost 
impossible. 
It is the special province of geological 
correlation to establish a general chrono- 
logic sequence for rock successions more or 
' less widely separated geographically. The 
main features of some of the more impor- 
tant standards of comparison that have 
been adopted or are being used may be 
briefly considered, their scope defined and 
their limitations noted. These methods 
fall into two main categories: (1) the 
strictly physical, and (2) the biological. 
Of these the latter have, for many years, 
been most widely followed. At the present 
time the former are beginning to assume 
much greater prominence than ever before. 
So profound an influence have the or- 
ganic remains entombed in the rocks had 
on correlation problems that it has only 
been very recently that the inherent weak- 
nesses of this criterion has begun to be ap- 
preciated. The advantage of the physical 
* Abstracted from a paper read before the Academy 
of Sciences of St. Louis. 
SCIENCE. 
655 
method over the biological is indicated by 
the remark made lately by McGee that 
“Nearly as much information concerning 
the geological history of the Atlantic slope 
has been obtained from the topographic 
configuration of the region within two years 
as was gathered from the sediments of the 
coastal plain and their contained fossils in 
two generations.” 
Indeed, for more than a score of years 
that branch of geology ealled stratigraphy 
has been practically at a standstill. 
methods are the same that were used 50 to 
75 years ago. However, the science of ge- 
ology as a whole has made gigantic strides. 
Within the last two decades several entirely 
new branches have sprung into existence. 
New and refined methods of working have 
been formulated. With all this activity 
going on about it, stratigraphy itself has 
been at last provided with new weapons 
of offense and defence, and is beginning to 
experience a revival that is surely destined 
to restore its old time prestige. 
The scope of the purely physical criteria 
of correlation and of geological classifica- 
tion as set forth in late years appears to 
have been generally overlooked. Attention 
needs to be called only to a few of these. 
Irving and Van Hise have formulated ad- 
mirable methods of correlation, in which 
organic remains are left entirely out of con- 
sideration. McGee and his colleagues have, 
by purely physical methods, attacked the 
unfossiliferous deposits of the coastal plain 
and then have applied the same methods 
successfully to the fossiliferous terranes. 
Davis and others have rejuvenated the old 
methods of stratigraphical continuity and 
lithological similarity, by making possible 
a system of correlation by geographic forms, 
and broad areas are now being geologically 
mapped by this method alone. All of these 
methods are more or less complex and not 
simple, but they demonstrate that newer 
and more natural ways are rapidly replac- 
Its 
