652 A. J PIESE 
qualifying adjectives, however, and attention to the order of their 
arrangement, would be valuable. Arenaceous glauconitic lime- 
stone should not be used when glauconitic arenaceous limestone 
is meant. 
8. Luster —Only occasionally does one find such remarks as 
“vitreous sediments,” ‘‘clayey surface,” etc. Perhaps luster has 
no great significance. Yet might not freshly exposed rocks be 
said to have vitreous, subvitreous, dull, earthy, etc., luster ? 
9. Lateral variation.—The importance of this factor can hardly 
be overemphasized. Any complete description of the‘‘ Fountain 
conglomerate” of the Front Range, e.g., would at once raise doubt 
as to the ordinary explanation of its origin. 
It will be at once remarked that none of these characters throws 
so much light on the history of a formation as does, say, the mere 
mention of drying-cracks.1 May that not be because drying- 
cracks have been studied by a geologic genius? The trouble with 
our field descriptions is that we incline to note only the unusual. 
Moreover, the extension of the writer’s list to include drying-cracks, 
ripple marks, jointing, topographic result of erosion, and other 
matters, would defeat his very practical aim. An elaborate sched- 
ule cannot be recalled in all its ramifications. The simple list here 
advocated can be easily mastered. 
THE NAMING OF SEDIMENTARY ROCKS IN GENERAL 
As stated, no attempt is made to present a complete classifi- 
cation of sedimentary rocks. It seems possible, however, to group 
all sedimentary rocks as follows, partly by the aid of field observa- 
tions, partly by microscopic examination: 
A. ORGANIC— 
1. Calcareous rocks 
. Ferruginous rocks 
. Siliceous rocks 
. Carbonaceous rocks 
5. Rarer types 
1 => &W ND 
«There is a further educational value in detailed, systematic description. In 
courses in advanced general geology, students are often required to make vertical 
sections based on folios, etc., and even to describe formations in class. If descriptions 
are so meager that students cannot visualize the sections they describe or construct, 
is not the value of such work greatly vitiated ? 
