

[No. 8. 3 
34 AN  (Gnieorin, 

Between these and the true great migrations there are all 
kinds of transitions. 
If the conditions favourable to birth continue for two suc- 
ceeding "years, the numbers of individuals may increase to such 
an extent that å great migration will supervene. 
It has hardly ever happened that å prolific year (and the 
consequent migration) has simultaneously embraced the entire 
land. The rule is, that the increase takes place in great or small 
districts independent of each other, but the area which may be 
involved thereby may be of very considerable extent. Occasion- 
ally the increase will take place simultaneously in two separate 
districts, divided from each other by an area of greater or les- 
ser extent, in which the production is normal. 
In Norway there may be recognised on the whole, at least 
5 great groups of mountains within which most of the migra- 
tions have their radiating centre. One migration may embrace 
either the entire group, or small portions of it. 
These great radiating-centres are as follows: 
1. The mountain plateaux of the Jotunheimen, and Lang- 
Fjeld, which send their swarms down to the western por- 
tions of Christiania Stift, Christiansand Stift, and the ad- 
joining parts of Bergen Stift. 
2. The plateau of the Dovre Fjeld, with its continuations the 
Gudbrandsdal and the Österdal mountains, as well as the 
mountains of the Romsdal to the North. From these parts 
the swarms cover both the northern distriets of Christiania 
Stift, as well as the adjoining portions of Trondhjem Stift as 
far as the Trondhjem's Fjord (ineluding Romsdal and Sönd- 
möre). 
3. The frontier mountains in Nordre Trondhjem's Amt send 
the hordes westward, over the entire county (as well as east- 
ward into the Swedish province of Jemtland, down to Åp 
Gulf of Bothnia). 
4. The mountains of Nordland, from which the exodus reaches 
the coast and its islands in the west, and spreads east- 
wards over the Swedish province of Lapmarken. 

