Review of Recent Geological Literature. 313 
have deported itself like the volcanoes of Tertiary and later times, 
With a little volume like this one as a touring companion, the sum- 
mer visitor to the coast of Maine may add a great deal to the pleasure 
of his outing.* Wi Si, B) 
The physical effects of contact metamorphism, JoserH BaARRELL (Am. 
Jour. Sci., vol xiii. Apr. 1902. pp. 279-206.) 
Dr. Barrel reaches some important results that go to elucidate some 
of the obscure and unstudied changes that take place in sedimentary 
rocks when brought into contact with igneous intrusives, He alsa gives 
data from which it can be determined what was the nature of sedi- 
“mentary rocks from which given metamphoric minerals have been 
derived. He finds that remarkable changes take place in mass and 
volume where sedimentary rock is metamorphosed, the loss in vol- 
ume sometimes reaching 47 per cent, and in weight nearly 30 per cent. 
The following table and accompanying observations are taken from 
his article: 
Relation of metamorphic minerals to original composition —From 
the species and proportionate amounts of the metamorphic minerals 
seen in thin section, it will be desirable to determine the nature of the 
original sediments and thence the changes undergone in mass, vol- 
ume and mineral composition. Leaving aside for the present those 
possible accessions connected with impregnation and fumarole action, 
the chemical elements will remain present as before stated except for 
the expulsion of a greater or less quantity of water and carbonic acid. 
To determine this relation of metamorphic minerals to original compo- 
sition, some definite basis must be adopted. For that reason the sedi- 
ments are assumed to consist of a number of stable minerals, the results 
of thorough decomposition. As has been shown, in argillaceous rocks 
such a condition is never perfectly reached, and where such have suf- 
fered changes the losses computed on the above basis must be dimin- 
ished by a factor depending upon the incompleteness of the decom- 
position of the original rock. In strata consisting of quartz sand and 
carbonates, however, the changes will be strictly those shown by the 
following table. ; 
The metamorphic minerals given in the table, except for the omis- 
sion of biotite, are those of commonest occurrence in strata adjacent 
to igneous rocks. Biotite, though of common occurrence as a result 
of metamorphism in rocks of an arenaceous-argillaceous character, 
has such a complex composition that it is useless to attempt to com- 
pute from what materials it has come, unless something is known of 
-the unmodified strata. The ferrous oxide, magnesia and alkalies pres- 
ent in biotite, furthermore, are indicative of an incompletely decom- 
posed sediment, and add to the difficulties. The absence of biotite 
from the table for that reason, however, is not a serious matter, since 
* Since the original report on which the present edition was based had a 
very limited circulation and since copies of it are not now available, it may be 
of interest to know that copies of the present edition are purchasable from 
the Registrar of Colby College, Waterville, Me., at the price of 50 cents each. 
