312 
decreasing basicity’ must point to some universal and not to 
any local causes. 
We may now consider the question whether one should 
seek the universal cause for the ‘rule of decreasing basicity’ 
in the processes of differentiation which belong to ‘the first 
order’. 
The age of an igneous rock, and its place in the chrono- 
logical sequence, is assumed at the time of its consolidation, 
and the observations from which the relative age of two asso- 
ciated abyssal rocks can be inferred, are of the phenomena at 
the contact between the two rocks (apophyses, variations in 
size of grains, cutting off of structural planes etc). Hence it 
must follow that the sequence, found by observation, is really 
the sequence of consolidation and nothing more. This view 
was clearly enunciated in some of the earlier statements about 
chronological sequence of Plutonic rocks’. But in the later 
literature the sequence of consolidation is freely considered as 
synonymous with the sequence of intrusion or sequence of 
coming to place, which with abyssal rocks may be something 
very different. The sequence of intrusion in turn is by pure 
hypothesis often referred to a sequence of differentiation within 
the supposed common magma reservoir, and thus an apparent 
connection is postulated between the order of consolidation 
of contiguous abyssal rocks and the hypothetical differen- 
tiation processes which operate in the deeper portions of the 
earth crust. 
It has already been observed by many petrologists that 
the differences between the age of associated abyssal rocks 
are often very small. Thus Daxyys and Тед, speaking of the 
1 Daxyns and TEALL, Quart. Journ. Geol. Soc., vol. 48, 1892, р. 106 
(“Taking all facts into consideration, there seems no escape from the 
conclusion that we have in this area the record of a series of events 
connected with the consolidation of a vast subterranean reservoir of 
molten rock” [the italics are ours)). 
