152 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
LITHOLOGY oF THE RoxBURY AND NEIGHBORING CONGLOMERATES. 
Metnops or Worx.—More than two hundred specimens from 
the Roxbury and neighboring conglomerate regions have been ex- 
amined in the laboratory. All of these have been studied by using 
the hand Jens on natural fresh and weathered surfaces. Polished 
surfaces of fifty or more specimens, typical of their respective local- 
ities, have also been examined with low and higher power lenses. 
The polished surface affords a very effective means for the study of 
many crystalline or clastic rocks. If the specimen is not too large it 
may be placed with its tray on the stage of a petrographic microscope. 
Then, with low power lens and reflected light, minerals and struc- 
tures may be observed which are not well discerned in ordinary mac- 
roscopie study. If the specimen is not so shaped as to lie with its 
polished surface horizontal, it may be placed in atray of sand, which, 
if carefully handled, will obviate the difficulty without endangering 
the microscope. A magnifying glass, mounted on a stand fitted with 
ball and socket joints, may be used with advantage to concentrate the 
light on the portion of the specimen to be inspected. This process has 
been employed by the writer in a number of cases. It possesses an 
advantage over the use of the thin section in that it permits the study 
of a larger surface of rock. The latter method, however, must still 
be applied in cases where minute details and careful determinations 
are required. More than fifty thin sections have been obtained and 
examined in connection with their respective specimens. 
SCHEME or Descriprion.— In the accounts of conglomerates in 
the preceding chapter the writer has often found it difficult to secure 
the details needed for the present discussion. The rocks have been 
described by some of the writers in a somewhat haphazard fashion 
rather than in accordance with a definite plan. Some looseness, 
or at least indefiniteness, in the use of descriptive terms has often 
left doubtful the exact meaning of a given expression. For ex- 
ample, the term “well rounded” as applied to the shapes of pebbles 
is occasionally misleading. It was noted (page 117) in Johnson’s 
description of the gravels of the High. Plains that the pebbles are 
described as well rounded when in the photograph accompanying 
his account they appear subangular. Thus it is highly desirable, 
when the lithological character of rocks, or indeed when any object of 
scientific interest, is to be described, that some definite plan be formu- 
