o23 Reviews—A: Réenard—On the Ardennes. 
that a few more names might with advantage have been placed 
upon the geological map. The names of the Vermilion Cliffs, for 
instance, and of House Rock Valley, important features often referred 
to, are not to be found. The map may be said in a certain sense to 
be “faultless,” because the faults are omitted. They are, however, 
laid down in the atlas on a different map, on which the stratification 
is not marked, but are not inserted in that which gives it. This 
appears to be a sundering of matters that should be conjoined. We 
also desiderate a divided scale of miles. 
Captain Dutton has worthily treated a noble subject. Every 
reader must feel his knowledge of the ways of nature largely 
increased by a careful study of this book. It conveys to us all 
a sometimes much needed warning, that there is a good deal to be 
known of which we know little. .We look forward with the expecta- 
tion of further instruction and delight, which we are sure will not be 
disappointed, from the results of his future explorations, in which 
we trust Mr. Holmes will accompany him. O. FIsHeEr. 
V.—RE&cHERCHES SUR LA COMPCSITION ET LA STRUCTURE DES 
PuynLuapEs ARDENNAIS, PAR A. Rénarp. Extrait du Bulletin du 
Musée Royal d’Histoire naturelle de Belgique. (1882.) 
HIS is a pamphlet of 385 pages, but though short it contains 
an immense amount of information, and that, too, on a most 
obscure and difficult subject, where the ill-defined minerals in the 
schistoid masses present a thick tissue of interlacing lamelle, which 
almost defies the microscope. This portion is mainly chemical: the 
microscopic details are to follow. 
The specimens have been mostly obtained from the “massif” of 
Rocroy in the French Ardennes. The author gives an outline of the 
history of the investigation previous to the well-known work of 
Sauvage, alluding to the idea of Omalius d’Halloy that these schists 
were steatitic. 
Mons. Rénard concludes as the result of the combination of 
chemical analysis and microscopic research that the “phyllades” of 
the Ardennes are formed, in variable proportions, of three essential 
elements. | q ) 
1. A micaceous substance which constitutes the base of these 
rocks, and is tolerably constant in amount. Its formula corresponds 
to that of sericite, H, (K.Na)? (Al,)? Si® On, 
2. A substance containing protoxide of iron and magnesia, and 
approaching chloritoid, whose formula may be stated as H, R(Al*) 
SiO,, where R is Fe and Mg. This occurs in greenish lamelle and 
filaments, and is more variable in amount than the other substance. 
3. Free silica, as quartz or chalcedony. The accessory minerals 
are magnetite, specular iron, pyrites, pyrrhotine, ottrelite, fibro- 
lite (?), rutile, tourmaline, zircon, and garnet, along with carbon- 
aceous matters. 
The author states the rules by which he has been guided in 
estimating the quantities of these minerals, together with an explana- 
