MANSFIELD: ROXBURY CONGLOMERATE. 139 
Color: — general tone of the rock; relations to matrix; relations to 
pebbles. 
Characteristics of Bedding: — uniform series grading into finer beds, 
thickness and extent; variable series (lenses of coarser and 
finer materials, false-bedding, and local unconformities, ripple- 
markings, sun-cracks, raindrop impressions, or organic mark- 
ings), thickness and extent. 
Relations to Subjacent Rocks: — conformable: nature of the under- 
lying series; unconformable: eroded surface deeply dis- 
integrated, eroded surface of relatively fresh rock unglaciated, 
eroded surface of relatively fresh rock glaciated. 
Under each of the major headings of the scheme each kind of con- 
glomerate will be considered briefly, with reference to the minor 
headings, as the data will permit. 
Matrix: — Marine. In the Texas example of marine conglomerate 
the matrix is described as ferruginous, gritty sand. Stratification is 
only indirectly implied. In the Pottsville conglomerate where the tran- 
sition to the underlying Mauch Chunk shales occurs, the matrix con- 
sists of coarse arkose sands. For a long distance above the base it is 
composed of micaceous, chiefly arenaceous material, poorly cemented 
and often containing some argillaceous coloring matter. Near the 
upper part of the section coarse gray sand forms the matrix. Both 
Composition and assortment are variable near the base but more uni- 
form near the top. hese characteristics tend to ally the Pottsville 
more closely with fluviatile than with marine deposits, as already 
noted. 
: —Fluviatile. The foregoing citations do not furnish much 
explicit data with reference to the composition and character of the 
matrices of fluviatile conglomerates, but in the descriptions of the 
extensive accumulations of southern Asia and the western part of the 
United States it is shown that the pebbles of the conglomerates rest in 
& matrix composed of materials of varying nature and size, which are 
often only imperfectly sorted and stratified. 
: — Lacustrine. No specific data with reference to the matrices 
of lacustrine conglomerates have been found. 
——:— Estuarine. In the case of estuarine conglomerates also 
little direct information was obtained. From Willis’s account of the 
characteristics of the Devonian sediments it would appear that an 
unassorted mixture of sandy and clayey particles may be expected 
to constitute the matrix of estuarine conglomerates. This expecta- 
tion is verified in the account of the tidal’ flats of the Severn, given 
by Sollas. 
