Review of Recent Geological Literature. 335 
They omit the well known process for determining the hardness of 
water by means of a standard soap solution, as it has been found to be 
unreliable in certain cases, and they give Hener's method instead, 
which has been found to be of more general application. 
The book is not overloaded with processes, but on the contrary con- 
tains but a limited number, well chosen, and rearranged in a very 
comprehensive manner. 
Bommelden og Karmoen med omgivelser geologisk beskrevne, af dr. 
Hans Reusch, Kristiania, 1888 ; 442 pp. Svo, with three colored maps 
and 205 text illustrations, and accompanied by an English summary of 
the contents. In this work special interest is attached to the dis- 
cussion of compression and stretching of the rocks. These phenomena 
are seen most distinctly in the fossiliferous strata and in the conglom- 
erates. The fossils and pebbles are pressed flat, or sometimes they 
are stretched in length in one distinct direction. The arrangement of 
the folia of mica in gneiss in parallel bands is attributed to stretching. 
This band structure is said to be often independent of the dip 
of the gneiss. Instances are given of gneiss with a conglomerate 
bedded in it, both being stretched in the same direction, making it 
evident that the gneiss is really stretched. Compression of granitic 
rocks is said to have given rise to gneiss-granite and porphyritic gneiss. 
The former is a foliated rock having the mica laminae in parallel position. 
A very coarse-crystalline pegmatite vein is illustrated showing folia- 
tion caused by pressure. The stretching structure in the granitic rocks 
is seen either combined with foliation or without it. The rocks in the 
latter case show a certain parallellism in the arrangement of the com- 
ponent minerals on faces running in the stretching direction. Faces 
running across it have a much more granitoid appearance. 
Many instances of conglomeritic structure in granitic masses are 
mentioned. The following is one of the descriptions of such a struc- 
ture (p. 411.) 
" On the farm Orevik, on the eastern coast of the Bommels is ob- 
served a peculiar rock "VVe see a grantilar crystalline, gray, granitic 
rock, stained with dark spots where the biotite occurs rather abund- 
antly. In the same mass also occur distinct rounded fragments of fine- 
grained gray gneiss, feldspar-bearing quartzyte and white quartz. The 
fragments are often as big as a man's head, sometimes still bigger. 
The fragments of quartz have very sharp contours ; the contours of the 
feldspar-bearing are not quite so distinct quartzyte. Still more welded 
in the surrounding rock are the gneiss-fragments, especially a granular- 
crystalline variety rich in biotite. The larger fragments of the latter 
appear like dark patches ; as to the smaller ones we are in doubt 
whether we have before us true fragments or only occasional spots rich 
in black mica in the usual granite. In the northern part the ground 
mass assumes a parallel structure, and there the doubtful fragments 
show curved forms clearly due to motion in the mass. The rock des- 
cribed gradually merges, by loss of fragments, into common granite. 
