648 SH LS VOCE 
©.10-0.12mm., sometimes it reaches 0.15-0o.20mm., and quite 
exceptionally even rises to about 0.3-0.4mm. In oliviniferous 
rocks with bytownite, the thickness increases to a still larger 
amount, and exceptionally, in deep-seated rocks containing much 
basic plagioclase, the whole quantity of olivine may even be spent 
in forming the zones. 
6. The total chemical composition of the zones is equivalent to 
the chemical composition of olivine plus plagioclase. 
It should be particularly emphasized that the zone next the 
olivine consists of hypersthene, which may be chemically considered 
as olivine less half the contents of MgO+/FeO, whereas the zone 
next the plagioclase consists of hornblende to which in most cases 
is added some spinel, which may be accounted for by the composi- 
tion of the plagioclase with some addition of MgO+FeO. 
The coronation of the olivine against the plagioclase—or, as it 
may be quite properly expressed as well, the coronation of the 
plagioclase against the olivine—is a phenomenon belonging to 
the solid phase of the minerals after finished crystallization. My 
son, Th. Vogt, state geologist, has pointed out to me that to 
these contact-new-formations the common physicochemical laws 
concerning the reaction between two solid phases are fully applicable. 
This reaction is advanced by high temperature, and besides is a 
function of t#me. Therefore it must be assumed that the corona- 
tion began to take place immediately after the formation of the 
two minerals reacting on each other, and went on down to a certain 
limit of temperature (by way of example, 900°, 700°, 600°, or 
perhaps lower). The more slowly the cooling took place during 
the interval of reaction, the more the reaction was intensified. We 
accordingly always meet with reaction rims between olivine and 
basic or intermediate plagioclase in deep-seated rocks, but not— 
or to a much less degree—in the dike and effusive rocks which 
were more quickly cooled. 
tSee Beyschlag-Krusch-Vogt, Erzlagerstattenkunde, Vol. I (2d ed., 1914), p. 122. 
I beg to point out that the physicochemical laws for the reaction in the solid phase 
will no doubt throw quite a new light on numerous geologic processes, particularly 
on dynamometamorphism and contact-metamorphism. Upon these processes the 
influence of the varying relations of time, pressure, and temperature will particularly be 
felt. 
