IOWA ACADEMY OF SCIENCES. 139 



Inadequacjf 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 w^e 

 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 Wads worth* 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. '' 



Gilbertt 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 



*BuU. Mus. Comp. Zool., vol. VII, p. 563, 1884. 



+U. S. Geo]. Sur., Bull. 81, p. 43:h, 1891. 



$Cong-. geol. international, Compte Rendu, 5me Sess., 1891, p. 153. 1893. 



gCong. geol. international, Compte Rendu, 4me Sess., 1888, App. B., p. 9, 1891. 



