At Black Carts farm, which the Wall now passes, the first turret discovered on the line of the Wall after the excavations had begun, and interest in the subject was revived, was here laid bare by Mr. Clayton in 1873.  At Limestone Bank, not much further on, the fosse north of the Wall, and also that of the Vallum, show a skill in engineering such as we are apt to fancy belongs only to these days of powerful machinery, and explosives for rending a way through the hardest rock.  The ditches have both been cut through the solid basalt, and great boulders of it are strewn around; one huge mass, weighing many tons, has been hoisted out—­by what means, we are left to wonder; and another, still in the ditch, has the holes, intended for the wedges still discernible.

A mile or so 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.