BY R. M. JOHNSTON, F.LS. 119 
disappointing” in view of the astronomical theory put 
forward, he nevertheless has practically* to admit thata 
glacial epoch cannot take place without the concurrence of two 
great causes, viz., a period of great eccentricity of the earth’s 
orbit, with winter in aphelion, conjoined with specially 
favouring geographical conditions. 
IMPROBABILITY OF FINDING EVIDENCE OF INTENSE GLACTIA« 
TION IN ANY Portion oF AUSTRALASIAN LOWLANDS 
amone Rocks oF THE SAME AGE WITH THE GLACIAL 
Eprocu or NortH anp CenTRAL Europe anp Norte 
AMERICA. 
There are some enthusiasts who are so infatuated by the 
supposed omnipotence of the astronomical theory when 
regarded as the sole cause of glacial epochs, that they are 
somehow imbued with the idea that the same cause or causes 
which produced the Till or “ Grund Moraine” of the northern 
glacial epoch in the lowlands of Scotland, Wales, and 
Ireland, between north lat. 51° to 59°, and covered these 
countries with a continuous ice sheet, may also be expected 
to have produced similarly intense results of glaciation in 
south lat. 36° to 38° in the lowlands of Australia, im a 
region corresponding to North Africa and the middle of the 
Mediterranean Sea in the Northern Hemisphere. 
Now, while it is granted that the actual facts of observation 
may be faithfully recorded by persons holding such ex- 
travagant notions, it may be doubted whether they are able 
to draw inferences from the less perfect. portion of supposed 
glacial evidence without being coloured to some extent by the 
extravagance of their ideas concerning the potency of causal 
influences. 
If we are to be guided by the true scientific method in the’ 
investigation of the potency of causes relating to climate and 
glaciation, we must surely proceed in a reasonable manner by 
deducing the unknown from the known, the past from the 
present. ‘ 
Now the potency of the causes which produced the glacial 
epoch in northern and central Hurope have been fairly gauged 
by very able observers; and they have not only closely deter- 
mined the limits of the spread of the northern ice sheet in’ a 
southerly direction, but, by a careful chain of observation of 
the upper and lower limits of iceaction on elevated slopes of 
mountains in a series: of latitudinal points, they have arrived 
at. a fairly approximate idea of the altitude of the glacial 
epoch névé or snow line; and from such materials have given’ 
* Ibid. 134, 159, 160. 
