The Stady of yatnvdl Palimpsests. — Gn'vislei/. 17 
In the process of adjustment, of the minerals or rocks to 
changes in their environment new elements are often added 
and old ones removed. If the changes take place at the sur- 
face of the earth, under ordinary atmospheric or aqueous in- 
fluences, they are included under the term ireathering and the 
result is usually disintegration. True metamorphism is con- 
nected with igneous and dynamic agencies; and while the 
word was first introduced by Lyell in 1832, it was not clearly 
defined until 1846, when Durocher described metamorphism 
as the sum total of all modifications in texture or structure 
to which rocks in nature are subjected. Daubree limited the 
definition to those modifications whose causes were fire and 
water, and Beaumont added the agency of mineralizers. The 
word metamorphism is now cosmopolitan, though given dilfer- 
ent limitations by different authorities. 
American geologists from an early day have been prominent 
in this field of study. The pioneers composing the American 
metamorphic school, Hitchcock, Mather, Dana, Logan, Rogers 
brothers, were active students of these altered records and 
they made many valuable observations. The}'- all regarded 
the process of metamorphisni as confined to the sedimentary 
rocks, a view which long retarded progress in the work. 
When foliated or parallel structures were observed in meta- 
morphic rocks they were regarded as the old sedimentarj^ 
lines which survived the alteration: A voluminous literature 
descriptive of this limited field of altered sediments soon filled 
the shelves of science. 
Down to the year 1875 the province of metamorphic action 
was thus confined to sedimentary^ rocks. About this time ap- 
peared the epoch-making works of Heim in the Alps and of 
Lossen in the Harz, whereby it was shown that igneous rocks 
could be changed by metamorphic action. 
On account of the interesting and inviting problems con- 
nected with this study, it has attracted the attention of many 
of the 3^ounger workers; and the result has been a very great 
advance in our knowledge of these broken and crumpled 
rocks, though the vast field yet remains practically unex- 
plored. 
Metamorphisni may refer to any change in rocks, but it is 
restricted now to include the changes whose conditions lie in- 
