a” | 
‘i 
4 
J 
1848. | WESTON ON THE GEOLOGY OF RIDGWAY. 247 
will be better understood by a few extracts from the same paper. It 
is stated that “the great Ridgway fault is an wpcast fault, elevating 
on its south side into contact with the escarpment of the chalk those 
strata that would otherwise have dipped beneath it—particularly the 
Portland stone, nearly along the whole line which this fault traverses.”’ 
And again, referring to the part of Ridgway Hill now under consi- 
deration, it is stated that ‘“‘ at Upway, on the northern extremity of 
the general section and near the summit of the hill, the Portland 
stone covered with Purbeck beds occupies the south side of the fault 
and nearly horizontal chalk on its north side, the Purbeck and Port- 
land beds rising at a high angle northwards towards the fault. From 
Upway for four miles westward to the final termination of the Port- 
land stone at Portisham, the Portland stone is continued to the south 
side, and the chalk to the north side of the fault. It is exposed by 
no section, but the junction can be traced on the surface of the 
fields.” 
From these extracts we learn— 
Ist. That the Portland stone was considered to abut directly 
against the chalk ; and 
2ndly. That although the existence of the Purbeck beds was di- 
stinctly marked, yet their deposition was understood to be upon the 
shoulders of the chalk, and not in any way intervening between the 
Portland stone and the chalk. 
In the same paper it is stated that “the Wealden or Hastings sands, 
after becoming gradually thinner in their progress westward through 
the Isle of Purbeck, terminate a little west of Lulworth.” This place 
must be about twelve or fourteen miles east of Ridgway, and there- 
fore the existence of the Wealden or Hastings sands so far west as 
Ridgway must be considered a new feature in the geology of this part 
of Dorset. 
If we refer to our authors’ surface-map we shall find the tertiary 
marked as existing near Came Down, and then not to be met with 
west of that locality until after a long-denuded interval it reappears 
on the high land of Blackdown. On ascending however the chalk 
hill of Ridgway, a little to the east of the intended railway, I found 
evident proofs of the presence of the supercretaceous deposit. I there- 
fore endeavoured to trace its continuity westward, and was led to con- 
clude that it actually reposed upon the chalk immediately above the 
tunnel now in progress. The inquiries subsequently made at the 
engineer’s office, respecting the nature of the strata passed through 
in sinking the great vertical shaft, quite confirmed my views: I found 
that about sixty feet of tertiary had been pierced defore reaching the 
chalk. 
The remaining subject (I mean the existence of the Oxford clay in 
this locality) will be better understood after an examination of the 
section (p. 249) and a perusal of the subjoined explanatory facts. 
_ The cutting represented in the section les in a direction nearly due 
north and south, and is bounded on the north by the chalk of Ridg- 
way, and on the south by the public road, under which a short tunnel 
has been made. 
u 2 
