90 Reviews—K. Pettersen’s Geology of North of Norway. 
system of making a special name for the slightest variation is conveni- 
ent, yet in distinguishing varieties from species paleontologists are 
exposed to many errors. In the living world, when the descendants 
from a single type present differences, which do not prevent the pro- 
duction of fertile offspring with the parent form, they are considered 
merely as varieties of the same species; but when these differences 
are such as to prevent the production of fertile offspring, they are 
regarded as indicating a different species. In paleeontology not only 
are we unable to avail ourselves of this criterion, but it is difficult to 
guide ourselves by the analogies offered by existing animals, since 
there is an extreme inequality in the external characters separating 
varieties and species; as, for example, the varieties of the Dog 
differ more from one another than does the Ass from the Horse. 
“This shows that we can only approximate among fossil forms to 
the degree of difference indicating a variety or a species. But, in 
order to come as near as possible to the truth, we should adopt the 
following plan :—viz. that when the differences separating fossil 
animals are of no importance from an evolutionary point of view, we 
may be permitted to regard such animals as mere varieties of a 
single species; that is to say, that they were all probably capable of 
producing fertile offspring among themselves.” 
Numerous examples are then cited of differences which may be 
regarded respectively as varietal and specific; the different propor- 
tions of the limb-bones of the Pikermi Hipparions being given as 
an instance of the former, while the three digits of the European 
H. gracile as contrasted with the single one of the Indian H. sivalensis 
are instanced as good specific characters. 
In conclusion it is observed, ‘That whatever may be the difficulty 
in marking the distinction between fossil species and varieties, I 
consider this distinction as worthy the attention of naturalists. 
The history of past forms reveals, indeed, a succession of unde- 
finable differences (nuancés indefiniés), which the Divine Wisdom 
can codrdinate, but to desire to mark each of which by a special 
name is to only prepare lists without end, in which human weak- 
ness must lose itself!” 
We cordially agree with these concluding remarks, and have no 
doubt that the author would extend them to embrace genera and the 
larger groups. The time has, indeed, come when we ought to 
accentuate the resemblances rather than the differences which we 
find among allied fossil forms; and to recognize that both in the 
case of specific and generic names it is advisable to use them in a 
much wider and less defined sense than we are accustomed to do 
when our study is restricted to the comparatively small fauna of the 
present day. Re: 
II.—DrEN NorD-NoRSKE rFJELDByGNING. , AF Karu PETTERSEN. 
Separataftryk af Tromsoe Museums Arshefter X. ‘Tromsoe, 
1887. 8vo. pp. 174, taf. i—iii. 
HE author has’ been engaged since 1865 in working out the 
geological structure of the mountain district of North Norway, 
