272 THE FORMATION 
tion, though even here the period is normally longer. The longest and most 
complex succession, however, may be accurately studied in a region, where 
several examples of the same succession occur in different stages of de- 
velopment. In the same region, the physical factors of one example of a 
particular succession are essentially identical with those of another example 
in the same stage. If one is in an initial stage, and the other in an interme- 
diate condition, the development of the former makes it possible to re- 
establish more or less completely the life history of the latter. The same 
connection may be made. between intermediate and ultimate stages, and it 
is thus possible to determine with considerable accuracy and within a few 
years the sequence of stages in a succession that requires a century or more 
for its complete development. In the Rocky mountains, gravel slides (talus 
slopes) are remarkably frequent. They occur in all stages of development, 
and the alternating slides of different ages furnish an almost perfect record 
of this succession. This method lacks the absolute finality which can be 
obtained by following a succession in one spot from its inception to final 
stabilization, but it is alone feasible for long successions, i. e., those extending 
over a score or more of years. When it comes to be universally recognized 
as a plain duty for each investigator to leave an exact and complete record 
in quadrat maps and quadrat photographs of the stages studied by him, it 
will be a simple task for the botanists of one generation to finish the investi- 
gations of succession begun by their predecessors. 
330. The relict method of studying succession is next in importance 
to the method of alternating areas. The two in fact are supplementary, 
and should be used together whenever relicts are present. This method 
is based upon the law of successive maxima, viz., the number of species and 
of individuals in each stage constantly increases up to a certain maximum, 
after which it gradually decreases before the forms of the next stage. In 
accordance with this, secondary species usually disappear first, principal 
species next, and facies last of all. There are notable exceptions to this, how- 
ever, and the safest plan is to use the relict method only when principal 
species or facies are left as evidence. An additional reason for this is that 
secondary species are more likely to be common to two or more formations. 
In the majority of cases, the relict is not modified, and is readily recognized 
as belonging properly to a previous stage. This is true of herbs in all the 
stages of grassland, and in the initial ones of forest succession. The herbs 
and shrubs of -earlier stages, which persist in the final forest stages, are 
necessarily modified, often in such a degree as to become distinct ecads, or 
species. The facies of the stages which precede the ultimate forest are rarely 
modified. The application of the relict method, together with the modifica- 
