TWENTY-NINTH ANNUAL MEETING. 129 
metamorphism. All of these alterations take place without any material change 
in the bulk composition. Static metamorphism, though not accepted by many 
geologists, has able defenders in such men as Hall, Judd, and Spring. Dynamic 
metamorphism has been firmly established by the classic works of Heim, Lehman, 
and Balzer. 
Metamorphism may be produced by the presence of some metamorphosing 
agent, and it is then termed contact metamorphism. The alteration in sur- 
rounding rocks may extend over a distance from a small fraction of an inch up to 
4,000 feet, as seen in the Pyrenees. The nature of the contact metamorphism de- 
pends on the duration of the action, the depth at which the alteration takes 
place, whether deep enough to prevent the escape of vapors and moisture, or not; 
and on the nature of the metamorphosing agent, whether it is a granite, diabase, 
or other rock; and also on the nature of the rock altered, whether crystalline 
schists, carbonaceous rocks, sandstones, or igneous rocks. The nature further 
depends on the structure of the rocks, whether foliated or not, as demonstrated 
in Brittany by Barrois. 
Rosenbusch, after careful examination of analyses, concludes that there is no 
change in the bulk composition of the altered rocks, though Michel Levy insists 
that there is always a very considerable addition of substance. 
The effect of contact metamorphism on crystalline schists is less intense than 
on most of the rock types. The effects, consisting mainly of the formation of 
new minerals, as andalusite, sillimanite, and garnets, have been described in the 
Cortlandt rocks by the late Dr.G. H. Williams. The effect of this form of meta- 
morphism on carbonaceous shales is to form a graphite, or the diamond, as in the 
South African region. The effects of contact action on clay slates have been de- 
scribed at a number of regions which serve as types: at Barr Andlau, in 
Germany, by Rosenbusch, by Lossen in the Hartz, by Allport and Phillips in 
England, by Barrois in Brittany, by Brégger in Norway. In these various re- 
gions it has been noted that the intensity of metamorphism at any given point is 
proportional to the nearness of the intruding rock. 
In limestone contacts the conditions are very favorable for the tracing of the 
beginning and development of the metamorphism. The limestone is observed to 
become more and more crystalline as the intrusive rock is approached and the 
carbonates change to silicates. These changes are observed in the well-known 
limestone contact region near Christiania, Norway, and the famous mineral lo- 
cality of the Fassathal, in the Tyrol. Contact action on igneous rocks has been 
observed at but few places. It has been described by Lossen in the Hartz moun- 
tains. 
The pioneer in the study of dynamic metamorphism was Lossen in 1867. In 
1878 Heim published his great work, the result of a long field-study of the Alpine 
rocks, in which he developed the theory that even the most brittle rocks under 
pressure acted as viscous bodies, and were deformed without rupture. Spring 
and Guembel endeavored to prove this theory by actual experiment, but the 
rocks were crushed to a fine powder. 
In 1884 Lehman, asa result of microscopical study of the crystalline schists 
of the Alps, concluded that the rocks were crushed and recemented under great 
pressure, thus producing an effect similar to viscous bodies, a process which 
might be described as rock regelation. These two works marks a new phase in 
the study of metamorphism the world over, through thé recognition of the fact 
that foliation in rocks is wholly independent of original structure. Parallel ar- 
rangement in rocks is not proof of sedimentation, a view which before this time 
was not recognized. 
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