MANSFIELD: ROXBURY CONGLOMERATE. 183 
(7) Cross-bedding is not common. The few examples_noted are 
widely scattered rather than limited to a particular region. 
(8) Ripple-marks and sun-cracks are also relatively rare but 
similar to cross-bedding in distribution. The ripple-marked layers, 
with perhaps a single exception, are in their normal position and are 
not inverted. No definite organic markings have been observed. 
(9) No actual examples of local unconformity have been seen but 
contemporaneous erosion is indicated by the inclusion of representa- 
tives of the series as pebbles in the conglomerate. The distribution 
of these pebbles shows that this feature is not confined to any particu- 
lar region. 
(10) The series appears to rest on an old land surface that had 
been deeply disintegrated by atmospheric agencies. No polished nor 
striated surfaces indicative of ancient glacial erosion were observed. 
Tar Norrotk Basın Srrtes.— Distribution: — Arkose. The 
known areas of arkose in the Norfolk Basin are confined to the 
exposures at Pondville in the southwest part of the field. 
:— Conglomerate. Conglomerate occurs in an apparently con- 
tinuous zone about half a mile wide along the south slope of the Blue 
Hill Range, from the Neponset River eastward to Great Pond in 
Braintree, and in more or less separated areas from Walpole south- 
west toward Pondville. 
:— Sandstone. South of the conglomerate zone an area of 
sandstone stretches east and west between the same limits and extends 
south as far as the railway cut about a mile north of the station at 
Canton Junction. Southwestward sandstone occurs in connection 
with the conglomerate in the manner above indicated. 
:— Slate. Slate or shale is not a conspicuous member of the 
series in the northeast part of the basin. It occurs toward the south- 
ern border of the sandstone area interlaminated and interbedded 
with the sandstone. The best exposure is found in the railway cut 
north of Canton Junction. Southwestward the slate assumes practi- 
cally equal importance with the conglomerate and sandstone and 
occurs in connection with them. The best exposure of the series in 
this region is at Pondville (Franklin VIII, K 29). 
: — Limestone. Limestone occurs at a single locality, the 
railway cut north of Canton Junetion. A small lenticular mass 1.5 
feet thick is interbedded with red sandstone and slate (Woodworth, 
b, p. 147). 
:— Associated Igneous Rocks. Igneous rocks are of little 
importance in the Norfolk Basin. The dike in the railway cut north 
