222 The American Geologist. March, 18&7 
the latter ineludiDg specific gravitj', simple reactions and associated 
minerals. The tables are arranged in the form of a key. showing (1) 
minerals of metallic lustre, which are further divided according to 
color, (2) minerals of sub-metallic and non-metallic lustre, divided fur- 
ther as to color of streak, and (3) minerals of non-metallic lustre and 
white or gray streak, divided further according to hardness. Following 
the tables is a supplement with the various minerals arranged in alpha- 
betical order, accompanied by their chief physical characters. A his- 
torical table of elements, scales of hardness and fusibility, and a very 
complete index finish the book. 
The above outline of the scope and plan of this book is sufficient to 
show its useful character and its adaptability to the general student, 
prospector or amateur, and also to the geologist who wants a ready and 
simple means of determining minerals in the field. The fact that these 
tables have reached their fourth edition shows that they are appreciated 
and widely used, and the improvements in this last edition besjjeak for 
it a much wider use. u. s. g. 
Geologic Atlas of the United States. Yellowstone National Park 
Folio, M^yoiiiing, JS'Jd. A general description introductory to the map 
sheets is given by Arnold Hague, treating of the geography, topogra- 
phy, and general geology. An outline of the characters and occurrence 
of the sedimentary rocks is presented by Walter Harvey Weed, and a 
similar chapter on the ig-a3ou3 rocks by Joseph Faxon Iddings. Three 
sheets of illustrations showing characteristic scenic, geologic, and topo- 
graphic features, serve as a further introduction to the maps. The at- 
las sheets are eight in number, four being devoted to the representation 
of topography with contour intervals of one hundred feet, and four to 
detailed areal geology. The scale is 1-125,000. c. e. b. 
CORRESPONDENCE. 
An explanation by Dr. Grimsley. Some criticism has been made 
on the article on the subject of Metamorphism in the January Geolo- 
gist, because due credit was not given the late Dr. G. H. Williams for 
the classification of metamorphic processes and the definition of the 
word gneiss. The definition of this last word was given by me in a 
former paper on the granites of Maryland, at the suggestion and with 
the full consent of Dr. Williams. The classification of processes was one 
used by him in his lectures, and while it is always a pleasui-e for the 
writer to yield homage to the memory and influence of that inspiring 
teacher, it seenied to him unnecessary in the present instance to reaf- 
firm this. The object of the article was to give in a popular style some 
insight into a difficult subject and to correct the improper use of cer- 
tain terms among many of our science teachers. As the article was in 
no way intended as an original contribution to knowledge, it was 
deemed best to omit all references to autliorities. G. P. Grimsley. 
Topeka, Kansas, Feb. 1, 1891. 
