198 Proceedings of the Royal Physical Society. 
deposition." We may, and must as far as we can, establish 
a similarity of order — homotaxis, as it has been termed — 
between the strata of different regions, but similarity of 
order is not to be confounded with synchrony of deposit ; 
and we must, therefore, if we would place the solutions of 
our science on a philosophical basis, abandon, as all sound 
geologists are rapidly abandoning, the idea that specific 
identity of fossil forms is proof of stratigraphical contempo- 
raneity. 
Quaternary accumulations. — Another point materially 
affecting the present position of our science, and one of 
the last to which our time will permit me to refer, is the 
very unsatisfactory arrangement of the post-tertiary, qua- 
ternary, or superficial accumulations. It is true we may 
generally classify them according to the agents by which 
they have been formed, or, in other words, according to their 
composition and the causes by which they have been pro- 
duced. In this way we have fluviatile, lacustrine, marine, 
chemical, organic, and igneous accumulations, but this con- 
veys no idea of succession or history in time. What our 
science requires is, that we endeavour to arrange them in 
chronological order, as we have done with the earlier sys- 
tems. The arrangement proposed by the late Dr Fleming 
into taragmite, akumite, and phanerite is so purely hypo- 
thetical, and so obviously at variance with observed facts, 
that it has not been, and cannot indeed be accepted. The 
broader arrangement into pre-human and human periods 
is obviously too general to be of much advantage to working 
geologists, at the same time that it can give us no clue to 
determine when the pre-human ends and the human begins. 
Again, such terms as the Leda clay" of the St Lawrence 
and the *' Saxicava sand" of Montreal, though good and dis- 
tinctive enough for local purposes, are inappropriate for 
other regions ; and others, as " Pampean formation," Erie 
clay," and the like, merely announce a geographical fact, 
without conveying any idea either of fossil remains or chro- 
nological sequence. Had the post-tertiaries, like most of 
the tertiaries, been strictly sedimentary, some percentage 
system of fossil forms like that by which Sir Charles Lyell 
