Review of Recent Geological Literature. 315 
the materials forming it have possessed but little carbon dioxide and a 
medium amount of water and consequently in metamorphism have 
not changed greatly in volume or mass. While the table shows in a 
general way and with a fair degree of accuracy the changes taking 
place to produce such minerals, for any special application it may be 
necessary to extend it in order to take in materials in the original 
sediments not here considered. The computations have been carried 
out with accuracy tothe final digit and therefore the only inaccuracies 
which would attend its use would be from a lack of definite knowledge 
in regard to the original and final composition of the sediments of any 
~ particular case. 
It is seen from the above table that wollastonite is produced from 
a siliceous limestone, diopside from a siliceous limestone containing 
some quartz. Vesuvianite commonly has a small part of its alumina 
replaced by ferric oxide, but here it is computed on an iron-free basis 
It is seen to be produced by a sediment not far in composition from that 
yielding grossularite, and has been observed together with it in rock 
sections. 
In epidote the aluminum and iron are interchangeable, the molecu- 
lar ratio of the two varying from 6:1 to 3:2. For this reason both zoi- 
site, the iron free epidote, and also the alumina free epidote molecule 
have their relations shown to the original sediments. If it is desired 
to find what sediments would furnish a given compound of the two 
molecules, it may be done by considering the ratio which is present in 
the mineral of the zoisite to iron epidote molecules and their respective 
molecular weights, that of the zoisite being 455, alumina free epidote 
451. In the same way any mixture of the albite and anorthite mole- 
cules may have its relations determined, the data of each being here 
given. ; 
The soda which is frequently shown to exist in hornfels by the 
presence of a soda-lime feldspar may have existed in unmetamor- 
phosed strata in a variety of forms. In fresh material it might occur 
~as a-soda-lime feldspar or feldspathoid, but these being somewhat 
readily decomposed it would more naturally be anticipated as a 
hydrous silicate, especially as.a zeolite. Merely to show in a general 
way the relations between an albite occuring in a hornfels and the zeol - 
ite minerals analcite has been selected. 
Orthoclase, being a mineral which often occurs in minor quantities 
in hornfelses, has been introduced for the sake of completeness. 
The greater part of it has probably come from yet undecomposed 
though finely comminuted orthoclase, which under the conditions 
of metamorphism has collected into definable crystals. Another part, 
however, is no doubt furnished by some of the many hydrous alkaline 
silicates reacting with other materials. 
Andalusite is seen to result from a clay upon the expulsion of the 
combined water, and is attended by the separation of a large amount 
of free silica, being the only mineral here considered which does 
not come from the union of two or more minerals of decomposition, 
but on the contrary breaks into two minerals during the process of 
