THE MEDITERRANEAN NATURALIST 
135 
Argynnis dia 
Pieris brassicae 
rapae 
Colias edusa 
Leucophasia erysime 
„ sinapis 
Polyommatus icarus 
„ telicanus 
Pamphila comma 
Tlianaos tages 
Fidonia atomaria 
Satyrus roxelana 
Hipparchia semele 
Epinephile hispulla 
Coenonympha pamphilus var. 
lyllus 
Melitae didyma 
Vanessa atalanta 
„ C. Album 
» Egea 
Limenitis Camilla 
Melanergia larissa var. 
Pieris brassicae 
„ daplidice 
Etrymon W Album 
Polyommatus icarus 
„ telicanus 
Pamphila sylvanus 
Thymelicus actaeon 
Zygaena filipendulae 
„ punctum 
Arctia villica 
Callimorpha jacobaem 
(to be continued ). 
Theories of Mountain Formation. 
BY T. MeLLAPJ) ReADE, C.E., P.G.S., F.R.I.B.A. 
Part IV. 
It will be understood from the principles enun- 
ciated in Part III. that the surface layers of the 
earth, are unaffected by expansion; it is only as 
they become buried in sediment that increasing 
heat can affect them. On the other hand, what geo- 
logical indications have we in them of the effects of 
the secular contraction of the globe? The con- 
tr&ctionists point to the folds of the great mountain 
ranges, but these, as already shown, only occur in 
areas of sedimentation. It would certainly seem 
that the secular contraction of the earth, if capable 
of producing these effects, should not be confined 
to areas of great sedimentation. We should expect 
to find old rocks in areas of denudation also 
thrown into folds and mountain ranges. As a 
matter of fact, no instance can be pointed to of a 
mountain range which has been entirely formed of 
old rocks. Old rocks are disclosed by the denudation 
of a range itself, but these have been the “foun- 
dation stones” of the range itself. 
If but one mountain range could be shown by 
the contractionists, to have been produced without 
the aid of sedimentation, their theory would be 
founded on a sounder basis of induction than it is 
at present. But it will be said, “even admitting 
the view that you take of the effect of secular 
contraction, and the existence of a level-of-no-strain 
in a cooling globe, the compression of the under 
layers of the earth must have produced some 
geological effects.” Secular contraction may have 
left its mark on the earth in some way not at 
present understood, and it will take a great deal 
of investigation of a less crude character than 
seems to satisfy some geologists, to settle this point. 
If, however, we consider that the layers of the 
earth in compression now — on the favourable 
supposition that the surface remains constant and 
unalterd except by such compression, which is the 
condition assumed in all the calculations of jthe 
depth of the level-of-no-strain — is at the maximum 
estimate under five miles, and the minimum under 
two miles deep, we get a clue to the absence of 
geological evidences of secular contraction. There 
are very few calculations of geological time — at all 
events by those who have studied geology — that 
put the earth’s history at less than 100,ot)0,000 
years, my own calculations being much in excess 
of that figure; (1) but for the purposes of mathe- 
matics one important condition in the calculation of 
the level-of-no-strain has been omitted, and that is 
denudation. I have pointed out in the “Origin of 
Mountain Ranges” that this agency would go far to- 
wards obliterating the geological effects of secular 
contraction. 
As a rule, those geologists who believe that the 
earth’s corrugations result from the contraction of 
the earth’s nucleus also contend that geological 
agencies, such as those producing denudation 
were much more active in the early ages of our 
planet, in which case a greater thickness of the 
earth’s crust must have been removed in a given 
time than what I am disposed to allow. Let us, 
(1) Chemical Denudation in relation to geolo- 
gical time , 
24.5.91 
to 
27.5.91 
and 
6.7.91 
Corfu 
