IOWA ACADEMY OP SCIENCES. 
139 
Inadequacy of Existing Methods. — ^It has already been intimated 
that the basis of geological classification has been, at various 
times, in accordance with very different standards and that 
these have continually changed. In passing from one to 
another, however, the change has been gradual and not abrupt. 
Being bound so inseparably to the past, it is well-nigh impos- 
sible for us to at once cast aside old ideas, even after we 
are fully convinced of their untrustworthiness. So, in clothing 
new conceptions in words, we unconsciously and unavoidably 
incorporate statements that are not only deceptive, but which 
have their foundation in error. Still, the expression of 
the new must be largely in terms of the old. In the dis- 
cussion of our standards of comparison, the old interpretations 
are naturally, yet unavoidably rendered, and more or less 
misunderstanding necessarily arises at first in the consider- 
ation of any new criterion. 
That every standard yet suggested for the determination of 
geological chronology has beeen inadequate, when taken 
singly, is conclusively shown by the practical tests that are 
being continually made. A satisfactory solution to the problem 
does not appear to be offered by any system yet proposed. It 
has almost come to be the despair of investigators. 
A few years ago, Whitney and Wadsworth* gave up all hope 
of unraveling pre- Cambrian geology without the use of fossils. 
Walcott, f after reviewing the methods of correlation in his 
correlation essay on the Cambrian, concludes that “For the 
determination of synchrony, except in a limited area, there is 
little hope for satisfactory conclusions by any method yet 
devised. ” 
Gilbert! states that at present “the legitimate use of physi- 
cal methods of correlation will necessarily be local * * * 
The value of a biotic group for purposes of correlation depends 
(1) on the range of its species in time and space, and (2) on the 
extent to which its representatives are preserved. ’ ’ 
Hughes, § in presenting the report of the British subcom- 
mittee on geological classification, clearly recognizes the fact 
that no one criterion is sufficient. “We must adopt the his- 
torical method * ^ * In geological history we must class 
together those results which naturally hang together, which 
*Bull. Mus. Comp. ZooL, vol. VII, p. 565, 1884. 
+U. S. Geol. Sur,, Ball. 81, p. 43H, 1891. 
$Cong. gdol. international, Oompte Rendu, 5me Sess., 1891, p. 153, 1893. 
§Cong. gdol. international, Oompte Rendu, 4me Sess., 1888, App. B., p. 9, 1891. 
