MANSFIELD: ROXBURY CONGLOMERATE. 185 
have been studied but have not been included in the following 
enumeration. They are entirely similar to the masses more cer- 
tainly in situ and it is believed that their exclusion will not materi- 
ally modify the proportions given. 
:—Bands. In the Norfolk Basin banding is again the prevalent 
type of bedding. Of the thirty-six outcrops recorded in the writer's 
field notes twenty-three exhibit some degree of banding. The areas 
where these features occur are not confined to any particular region 
but are generally well distributed throughout the basin. In some cases 
the banding is well defined and the several types of sediment are clearly 
bedded with no transition between coarser and finer materials. Such 
a condition is seen in some parts of the ledge southeast of Norwood 
(Dedham, I, X 32) where slate and conglomerate with pebbles one or 
two inches in diameter sometimes occur together with no gritty nor 
slaty bands between. In other cases the banding is very indefinite 
and irregular so that no sharp line of division can be drawn between 
the neighboring types and the attitude of the band can be determined 
only by its general appearance in the ledge. Sometimes the indefinite 
bands are narrow and may become mere streaks. The latter are, 
however, not abundant; only two or three cases have been noted. 
——:—Lenses. The occurrence of lenses in the Norfolk Basin has 
been observed in only four localities: in the gritty portion of the rocky 
ridge east of the Neponset River (Dedham IV, I J 25), in sandstone 
ledges in approximately the same strike east of Ponkapoag Pond (Ded- 
ham IV, Y 25), in the large masses of coarse conglomerate not certainly 
in place south of Bear Hill (Dedham VII, E F 18), and half a mile 
east of the last locality (Dedham VII, G 19). In all cases they are 
composed of red sandstone and are so small that little can be deter- 
mined with reference to their arrangement. 
:—Cross-bedding. Cross-bedding is even less common than 
lenticular arrangement. Only three cases have been observed and these 
are found toward the southern end of the rocky ridge above mentioned 
and in the large separated masses or ledges of sandstone at the north- 
west end of Great Pond. The best example occurs at the ledges on 
Pecunit Street in Canton (Dedham IV, I J 25). 
——:—Ripple-marks and Mud-cracks. Ripple-marks and mud- 
cracks have been observed at only one locality, the Pecunit Street ledges 
above mentioned. They are well exposed and show that the strata are 
not inverted. No traces of organic forms were seen on these surfaces 
but farther north in the same ridge, and farther south in the ledges at 
Pondville, traces of tree trunks or roots have been found, while in the 
