ioo6 The American NaUiralist. [No^-ember, 
and re-cementing. Analyses of phyllites, amphibolites, porphyroids, 
quartzites, and a few minerals from interesting localities in Belgium 
and the Ardennes, France, form the basis of an instructive article by 
Klement.-* Collins,^ in an article on the nature and origin of clays, 
divides these into clays produced in situ by the alteration of feldspar, 
and derived clays. The former are purest, and include the china clays. 
Derived clays are impure, in consequence of the admixture of unaltered 
feldspar and other minerals. The composition of a pure clay is about 
SiO, Al^Og FeP3 Alk MgO CaO Org. Mat H,0 
47-82 41.43 .30 .39 .29 .11 .10 10.50 
When washed, it contains no scaly or flaky particles, but possesses 
a uniform texture. Its composition corresponds very nearly to the 
formula Al, (HO)^ SiO.+Al.Oj 3810^. In discussing the origin of clays, 
Collins states that the theory based upon the action of carbon dioxide on 
feldspar is untenable. He inclines to the von Buch and Daubree view 
of the action of solutions containing salts of fluorine or fluosilicic 
acids. Teall^ has discovered long, acicular, colorless, rutile needles 
in several of the clays of England. This observation is interesting from 
the fact that Thurach was not able to find the mineral in the clays which 
he examined, although it is well known as a constituent in clay slates 
under the name " Thonschiefer-nadelchen." Among some notes on 
a few rocks from the Salzburg and Tyrolese Alps, Cathrein' describes 
an eclogite in which the garnets are changing to hornblende. He 
also mentions an amphibolite in which are light-colored apparently 
prismatic crystals, which, under the microscope, are resolved into 
aggregates of epidote and zoisite. The author regards them as pseudo- 
morphs of the former mineral after the latter. A second specimen of 
amphibolite contains garnets that are gradually changing into biotite. 
Mr. Merrill^ describes in detail the peridotite^ from Deer Island, 
Maine, in which augite enlargements have been discovered. The rock 
is a picrite, composed of olivine, augite and various iron oxides. The 
enlargement of the augite seems to have resulted in some way through 
the alteration of olivine, as the added material is found extending from 
