3. _Highly altered basic Tuffs, and agglomerates_ (calcareous
chloritic schists).--Only one stump now remains.
4. _Altered Rhyolites and Dacites._--Only fragments of this rock
have been revealed during Mr. Gowland's excavations in 1901.
At one time doubtless there was a whole upright of this
material, but its striking appearance and fracture has
probably led to its demolition by generations of _souvenir_
hunters. Other fragments have been found in the barrows once
within sight of Stonehenge, but now destroyed by cultivation.
5. _Sandstones, Grits, and Quartzites._--The "Altar-Stone" belongs
to this class. It is interesting to note that Professor
Maskelyne has pointed out the similarity between the Altar
Stone at Stonehenge, and the "Stone of Destiny" in the
Coronation Chair at Westminster Abbey.
6. _Grey Wackés._--Fragments only of these stones have been
discovered among the chippings incidental to the dressing of
the stones before erection.
Their absence at the present day is not a matter for surprise, as
stones of this class weather badly, and when exposed to the
action of frost and cold rapidly disintegrate.
7. _Argillaceous Flagstones and Slates._--As in the case of the
Grey Wackés, fragments only of these stones exist to tell the
story of the uprights which have vanished under atmospheric
changes.
8. _Glanconitic Sandstone_ (possibly Upper Greensand?).--Traces of
this rock have been discovered at Stonehenge by Mr.
Cunnington. Professor Judd suggests the possibility of a
boulder of this material having been found and used by the
builders of Stonehenge.
9. _Flints._--These of course are naturally found in abundance
throughout the district. Most of those found within
Stonehenge are broken fragments struck off in the process of
repointing flint chisels during the erection of the circle.
The above catalogue of stones may not convey very much to the ordinary
visitor, and has only been inserted for the sake of completeness; or
for the information of geologists who may be concerned with this
aspect of the history of the monument. The conclusions to be drawn
from such a list, however, are not without interest to the general
reader. From the varied fragments found, it is apparent that some six,
or perhaps seven, different classes of stone were used for the small
uprights, but that only the harder and more durable rocks (the
diabase, rhyolite, etc.) have survived. The softer rocks (basic tuffs,
grey wackés, flagstones, and slates), being more easily broken, have
fallen victims to the souvenir hunter, and to the action of the
weather, rain, and frost. Originally, as has already been stated, the
foreign stones numbered forty-five, disposed as follows: thirty in the
outer circle, and fifteen in the inner horseshoe. To-day only nineteen
exist in the outer circle, and eleven in the inner horseshoe.
A very striking proof that many of these foreign stones have
disappeared, is to be found in the wide gaps which exist to-day in
certain parts of the circle. That such gaps were originally filled by
standing stones is beyond question, indeed, the base of a "schistose"
stone (see Class 3 in the Lithology above) was actually discovered by
Mr. Cunnington in the course of his investigations into the nature of
the rocks composing Stonehenge. It is highly probable that careful and
scientific excavation may add greatly to our knowledge in this
direction.
There is yet one other point of interest in connection with these
foreign stones. On entering the circle from the north-east (the usual
path taken by visitors) a recumbent foreign stone will be noticed on
the left-hand side, which has two cavities worked in it. This is the
only worked foreign stone in the whole monument, and at first sight
these cavities may possibly suggest themselves as "mortise holes"
similar to those on the Sarsen trilithons, to be described later. It
has even been suggested that the small uprights once carried imposts,
or lintel stones similar to the trilithons, on the evidence of this
one stone. Such a theory, however attractive, should be accepted with
due caution, for the cavities on the stone are far from the ends, and
situated too close together to justify a comparison with the existing
Sarsen trilithons of the outer circle. This stone has never yet been
explained and its position defined, consequently it is omitted from
the frontispiece.