1881 .] 
211 
[Dodge. 
made at the time of deposition by sliding of the material depos- 
ited upon the lower beds. Strike 1ST. 8° E. — S. 8° W. Dip 
25° W. 
A line 177 yards long, projected at right angles to Codman 
Street at a point 147 yards from Dorchester Avenue, ends at a 
third exposure of slate. Here there is a south-easterly dip of 
about 50°. The strike, N. 88° E., points into the midst of the 
puddingstone quarry at a place many yards south of the north- 
ern limit to which puddingstone originally extended and still ex- 
tends in places. The slate mass is only 34 feet from the nearest 
exposure of puddingstone, and between the two occurs a little 
slate. There is, no doubt, a fault here or unconformable superpo- 
sition, and the line of division may be brought to view hereafter. 
Without additional exposures of the slate it cannot be certain 
that the strikes and dips observed are not local irregularities. 
The constant northerly dip found to the southward in the pud- 
dingstone and sandstone of the quarry; east of Washington 
Street, south of the M. E. Church near Richmond Street ; east of 
Dorchester Avenue on the east side of the puddingstone ledge 
between Richmond and Adams Streets : show that between the 
Codman Street quarry and the anticlinal which crosses the Hepon- 
set west of the Lower Mills, is an excellent opportunity for esti- 
mating the thickness of the beds of South Dorchester. 
The anticlinal axis which, as Mr. Crosby has already shown, ex- 
ists in the slate on the south side of the river west of Milton Lower 
Mills, there, obliquely crossing the railroad track, has an easterly 
dip of some 15° or 20°. The strata curve with great evenness. 
Occasionally measuring across the axis, an irregularity reverses 
the course of the progression of the strike-direction around the 
horizon, and in a few places a slip upon a joint plane accelerates 
the changes in the dip, otherwise uniform. The median line of 
the axis may be considered as crossing the track at about the 
middle of the curve in the cut. Following this line westward, 
we find puddingstone which no doubt underlies the slate in natu- 
ral succession. Along the south side of the track, eastward from 
a point in line with the wall which comes down from the school- 
house on River Street, to the northern bank of the river, the dip 
is from 40° to 75°. The strike about N. 48° E. — S. 48° W. The 
