DESCRIPTION AND NAMING OF SEDIMENTARY ROCKS 651 
advocated a list of points in the description of sedimentary rocks 
which, it is believed, should never be omitted. 
The list is as follows: 
1. Location.—Nothing is more provocative of time-wasting than 
for a second observer to search for a vertical section made “on 
Wolf or Cow Creek,” said creek being in a narrow canyon, 15 miles 
long. Various more accurate modes of statement readily suggest 
themselves. 
2. Name of rock.—This, a matter determinable partly in the 
field, partly in the laboratory, is later discussed. 
3. Massiveness or stratification—This should include mention 
of the average thickness of beds; or, if there are alternations, 
reference to average thickness for each type. 
4. Color, fresh and weathered—Names for color naturally 
involve a personal equation. Simplicity is often needed. Admir- 
able as are the descriptions of sediments in such a professional paper 
as No. 78, the amount of space devoted to refinements of color 
might well have been allotted to other details. ‘Too often the color 
of pebbles in a conglomerate is not considered apart from the 
color of the matrix; secondary color, whether of pebbles or cement, 
is not distinguished from primary, etc. 
5. Hardness—The employment of a mathematical scale, as 
with minerals, seems impossible. Hardness, however, is usually 
a result of cementation. The following terms are perhaps usable: 
(a) soft: rock easily broken between the fingers; (0) subhard: 
rock breakable by a light hammer tap; (c) hard: rock broken only 
by a sharp hammer blow; (d) superhard: rock dense and resistant 
to the hammer. Doubtless, strength of arm is here a factor; but 
the personal equation is less than with color. 
6. Size of grain.—In the field, measurements can rarely be 
made. Accordingly, exact limits for such terms as fine-grained, 
medium-grained, coarse-grained are not advocated. However, the 
term “‘pebble” should denote only material over a given size, say 
+ in. in diameter. The most inexpert assistant knows such terms 
as Oolitic, pisolitic, etc. 
| 7. Mineral composition—In the field, statement of mineral 
composition is seldom more than a guess. The use of proper 
