further on is Procolitia (Carrawburgh), where is the famous
well presided over by the goddess Coventina, whose acquaintance we have
already made at Cilurnum. The remains of the station at Procolitia are
by no means to be compared with those at Borcovicus or Cilurnum; very
few of its stones are yet remaining. The well was the most interesting
find at Procolitia. It was known to be there, for Horsley had mentioned
it; but the waters which supplied it were diverted in consequence of
some lead-mining operations. Then the stream formed by its overflow
dried up, grass grew over its course and over the well, and it was lost
sight of entirely. But the same thing which had led to its disappearance
was the means of finding it again. Some lead miners, prospecting for
another vein of ore in the neighbourhood, happened to dig in this very
spot, and soon struck the stones round the mouth of the well. Mr.
Clayton had it properly excavated, and was rewarded by coming not only
upon the well, but a rich find of Roman relics of all kinds, which had
either been thrown pell-mell into it for concealment in a moment of
danger, or, what is more likely, been thrown in during the course of
ages as votive offerings to the presiding goddess of the well. There
were thousands of coins, mostly silver and copper, with four gold pieces
among them; and a large collection of miscellaneous objects, including
vases, shoes, pearls, ornaments, altars and inscribed stones, all of
which were taken to Chesters. The next point of interest on the Wall is
the farmhouse of Carraw, which the Priors of Hexham Abbey once used as a
summer retreat. A little further on, at Shield-on-the-Wall, Wade's road
crosses to the south of the earthen lines, and parts company with the
Wall for a little while, for the latter bends northward to take the high
ridge, as usual, while the road and Vallum continue in a straight line.
The fragments of a mile-castle are standing just at the point where the
Wall swerves northward; indeed, we have been passing the sites of these
_castella_, with fragments more or less in evidence all along the route,
but those which we shall now encounter are much more distinctly to be
seen than their fellows on the eastern part of the journey, many of
which have disappeared altogether.

The high crags which here shoulder the Wall are part of the Great Whin
Sill, an intrusive dyke of dolerite which stretches from Greenhead
northeastward across the county nearl