-'^"^ T}ic A iitericd II (Teologixt. 
Novciiibcr, 1896 
tions in error. Still, the exi)ression of tlic new must be largely 
in terms of the old. In the discussion of our standards of com- 
parison the old interpretations are naturally, yet unavoida- 
bly, incorporated, and more or less misunderstanding necessa- 
vn\ arises at first in the consideration of any new criterion. 
That every standard yet suggested for the determination of 
geological chronology has been inadequate when taken singly 
is conclusively shown by the daily practical tests that are 
made. A satisfactory solution to the problem does not ap- 
pear to be offered by an}' 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 unravelling 
pre-(Jambrian geology without the use of fossils. Walcott,f 
after reviewing the methods of correlation in his essay on the 
Cambrian, concludes that "For the determination of synchro- 
ny, except in a limited area, there is little hope for satisfac- 
tory conclusions by any method yet devised." Gilbert]; states 
that at present "the legitimate use of i)hysical 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 ex- 
tent to which its representatives are preserved." Hughes,^ 
in presenting the report of the British subcommittee on geo- 
logical classification, clearly recognizes the fact that no one 
criterion is sufficient. "We must adopt the historical method 
* * * * . In geological history we must class togeth- 
er those results which naturally hang together, which belong 
more or less to one set of conditions as shown by the similari- 
ty of the inhabitants, as well as of the country occupied and 
of the structures which remain; that is of the fossils, the 
stratigraphy and petrology of the district. Our greater di- 
visions must be based on the more complete changes and the 
smaller uj)on the minor fluctuations, which will be indicated 
onl}' by the more sensitive and specially adapted forms of life, 
or by the more minute structural changes." 
*Bull. Mus. Cotnp. Zool., vol. vii, p. 565, 1884. 
tU. S. Geol. Sur., Bull. 81. p. 433, 1891. 
ifCong. geol. international. Couipte Rendu, 5ino Sess., 1891, p. 153, 
1893. 
^Cong. geol. international, Conipte Rendu. 4me Seas., 1888, App. B, 
p. 9. 1891. 
