THE QENEEAL WOUKINa SCHEME. 139 



group themselves ( one group consisting of old timber, another 

 of middle-aged timber, a third of young timber, and so on,) 

 determine the number and position of the Blocks, and, as a 

 consequence, the number and length of the Periods. I^ for example, 

 the silver fir forest taken for illustration higher up contained four 

 almost equivalent groups of crops, well defined on the ground 

 and presenting four principal age-groups, we would naturally 

 divide the Working Circle into 4 Blocks and the Eotation into i 

 and not 5 Periods. And as the figure there adopted for the Rotation 

 is not an exact multiple of 4, it would be necessary, if it was found 

 expedient to have equal Periods, to reduce or increase that figure 

 so as to make it an exact multiple, a conttngencj of little 

 consequence as respects a fir forest, which becomes exploitabk 

 towards the age of 150 years, more or less. 



In the case which we have been considering, we have supposed 

 that the four Periodic Blocks naturally marked out on the ground 

 are of equal extent or of equivalent productive power, and capable 

 of yielding the same quantity of produce when exploited each in 

 its respective turn for regeneration. A sustained yield is thus 

 assured, as far as that is possible, for the whole term of the Rotation, 

 and the Working Scheme drawn up on this basis fulfils the thre« 

 principal conditions it must satisfy.- 



It is seldom that the formation of the Periodic Blocks can b« 

 efiiected under such simple circumstances. For the most part the 

 crops belonging to the principal age-groups are not distributed in a 

 suflSciently convenient manner for this purpose ii» each Block. 

 Sometimes certain age-groups are even entirely wanting, so that, 

 in order to be able to secure a continuous series of exploitations, 

 there is no alternative but to collocate in the Period of the Rotation 

 corresponding to these age-groups, crops that are either too old or too 

 young for the purpose. In the presence of such difficulties and of 

 a great many others which it is impossible to enumerate, but which 

 are met with in nearly every attempt at forest organisation, the 

 Amdnagiste may find himself no little embarrassed. The conse- 

 quence is that it is difficult to arrange in advance for more than 

 one Period the succession of the Principal Fellings to be made in any 

 Working Circle, and still more so, to forecast the yield of each Period 

 of the Rotation. Nevertheless without seeking to effect a perfect 



