486 Dr. FE. Naumann—Magnetism and Earth Structure. 
which have been briefly summarized above, lead me to the following 
conclusions : 
1. While I would not venture to affirm that pressure has no effect 
in producing crystallization in a limestone, this is only small and 
subordinate, quite insufficient as a rule to obliterate the ordinary 
character of a limestone, such as occurs in strata of later Palaeozoic 
or of Mesozoic age. Certainly, as is shown by the study of limestones 
into which igneous masses have been intruded, the effects of pressure 
are far less marked than those of heat, under circumstances which 
appear to be otherwise similar. 
2. When limestone already crystalline has undergone severe 
pressure, its structure, macroscopically and to a considerable extent 
microscopically, is rendered less coarsely crystalline, i.e. instead of be- 
coming more distinctly crystalline, it is made to resemble more nearly 
an ordinary limestone (non-oolitic and unfossiliferous) such as might be 
obtained in Derbyshire, in South Devon, or in many parts of the Alps. 
Perhaps I should add that I am fully aware that some geologists, 
whose opinion is entitled to respect, have recently asserted that 
certain crystalline limestones in the last-named district are Jurassic 
rocks which have been altered by pressure. The typical instance of 
this, as it may be called, has long been known to me, and has been 
recently examined anew. It will take some time to complete the 
study of the specimens which have been added to my collection, and 
until that is done, I will say no more than that this identification 
appears to me an hypothesis, in support of which only a little and 
against which very much evidence can be adduced. 
Indeed, as I hope to show in a paper now nearly completed, which 
will include the results of this and other work in a like field, the 
direct effects of pressure are rather destructive than constructive— 
a matter which I think has sometimes been overlooked in specula- 
tions on ‘pressure-metamorphism.’ It is but a part of a chain of 
sequences, though here also it may be true that (to speak figura- 
tively) “mille animas una necata dedit.” 
IIJ.—Trrrestria, Macyerism as Mopiriep By THE STRUCTURE OF 
THE Hartu’s Crust, AND Proposats Concerning A MaGnetic 
SURVEY oF THE GLoBs.! 
By Dr. Epmunp Naumann. 
“TT\HE study of any new science,” says Alexander v. Humboldt, 
“may be compared to a journey to distant lands. Before 
starting in company with others, the question as to the practicability 
of the journey is raised; while examining one’s own powers, the 
qualities of fellow-travellers are looked upon with distrust. It is 
feared—perhaps without just reason—that they might cause un- 
pleasant detention. In our time the difficulties of an undertaking of 
this kind are much diminished. Any confidence is founded on the 
bright blossoming state to which natural sciences have grown, their 
wealth being no more the abundant quantity, but the concatenation 
of what has been observed.” 
1 Read at the Brit. Assoc. Newcastle, before Section C (Geology), Sept. 1889. 
