MANSFIELD: ROXBURY CONGLOMERATE. 179 
Lenses of conglomerate and grit occur at other localities. The 
observed examples as seen in cross-section do not appear to form linear 
bundles nor imbricated masses, unless the arrangement indicated 
in Figure 4, C can be so considered. On the contrary, the lenses 
appear as separate, independent bodies with roughly parallel axes and 
lie in the same horizon or in parallel horizons. The available evi- 
dence, however, is so scanty that little reliance can be placed upon it. 
:—Cross-bedding. According to the observations of the writer 
cross-bedding is not an important characteristic of the sediments of the 
Boston Basin. Of the 283 outcrops recorded only seven show cross- 
bedding and even in some of these cases it is ill defined.. Usually this 
feature is associated with sandstone layers or lenses but in one or two 
instances it occurs in layers of grit. Well-marked examples are seen 
in the fine ledges on the north side of the railroad east of Newton 
Center (Boston V, U 1-2). An ill-defined case of cross-bedding occurs 
in the lens at Thompsonville (Figure 4, A). Other occurrences are 
found in the sandstones that accompany the conglomerate and slate 
in the railroad cut south of Chestnut Hill Reservoir (Boston VI, C 
1), in the sandstone and melaphyr ledges at Brighton: (Boston V, I 
28), in the sandstone and slate outcrops at Roslindale (Boston VI, I 
20), in the conglomerate and sandstone ledges by the Neponset River 
at Mattapan (Boston VI, W 28) and in the fine ledges in Melville 
Garden at Hingham (Boston Bay VI, G 32). The distribution of 
these examples indicates that cross-bedding is not a characteristic of 
any particular portion of the basin, but that it is, on the whole, 
equally distributed among the sandstones and grits throughout the 
basin. At all of the outcrops named the cross-bedding appears 
merely as a subordinate feature. 
:— Ripple-marks. Ripple-marks have been found in associa- 
tion with some of the cross-bedded lenses above mentioned, as indi- 
cated in Figure 4, A. More commonly, however, they occur in 
connection with finer, more shaly sandstones. Only six cases have been 
„observed. Perhaps the best example is to be found in the quarry on 
Warren Street in Brighton (Boston V, G 28). There the ripple- -marks 
occur in fine sandstone, are sharply defined and appear in normal 
position on surfaces that dip gently north. A little less than a quarter 
of a mile to the east there is a fine ledge of somewhat shaly sandstone 
cut by a large mass of melaphyr. On the northeast side of this ledge 
rather indefinite forms occur which appear to be ripple-marks in an 
inverted position. The layers exposed seem to present the casts of 
the marks rather than the marks themselves. The apparent inversion 
