It is a principle in nature, that, when a globe is turned on its axis, the matter on the surface flies the contrary way to its motion. The philosophers call this improperly a conatus recedendi ab axe motus: it is not owing to an endeavour of matter to fly the contrary way, but to the innate inactivity of matter that resists the motion; does not readily follow it.
But it is evident from hence, that the earth, receiving its motion before the surface was perfectly consolidated, the moistish matter would be left westward, as far as it could be, and produce an extended and gentle declivity on the east; and at the same time, by stiffening, would render the west side of all hills steep.
This is a fact throughout the whole globe. Hence it is, that all plains and levels have naturally their descent towards the east; and hence it is, that the river of Witham, from Grantham side, running northward to Lincoln, readily takes its course thence eastward, to meet the ocean over the fenny level.
The Romans, when they made the artificial canal, the Carsdike, from Peterborough along the edge of the Lincolnshire fens, introduced it into the river Witham, three miles below Lincoln. The purpose of this artificial cut was, to convey corn in boats, from the southern parts of England, to the northern prætentura’s in Scotland for maintenance of the forces kept there: therefore the canal, entering the Witham, passed through Lincoln, and then was continued by another artificial cut, called the Fossdike, from Lincoln to Torksey, where it enters the Trent, in order to go down the stream to the Humber: from thence the fleet of corn-boats passed up the river Ouse to York, by force of the tide; for so high will the tide carry them; which was the reason of building the city there.
After this Fossdike, between the Trent and Witham rivers, was made by the Romans, it is easy to imagine, that the extensive river of Trent, which runs altogether northwards, would very readily, upon great floods, discharge part thereof into the Fossdike; for there is a descent that way, as being to the east: and this might be the occasion of the geography in our map, mistaking the Fossdike, and the continuation of the Witham, for that of the Trent.
The river Witham, from Lincoln, goes south-east into the sea, by Boston; and it seems to me, that in very early times it might (at least in great floods) have another channel running over the East fen (as called) along that natural declivity, full east, into the sea, as in the map of Richard of Cirencester.
This channel might pass out of the present river of Witham a little below Coningsby, where the river Bane falls into it, at Dockdike and Youldale, by the water of Hobridge, north of Hundle-house; so running below Middleholm to Blacksike, it took the present division between the two wapentakes, all along the south sides of the deeps of the East fen; and so by Blackgote to Wainfleet, the Vainona of the Romans.
My friend, John Warburton, Esq; Somerset herald, has some manuscripts of our Lincolnshire antiquary, some years ago, Mr. De la Pryme, who was perfectly acquainted with that part of Lincolnshire, and therein discovers some suspicions of the Trent running toward Lincoln in antient days; but I think, all we can certainly conclude from our map is the extreme antiquity of it: as the Carsdike must have been projected and done by Agricola, on his conquest of Scotland, we may reasonably judge this to be in the main his map, i.e. copied from his, though with some additions by our author.
This consideration, duly attended to, shows the antiquity of the Fossdike, and Carsdike, and of our map.
We are told in the History of Carausius, that he repaired the prætentura made in Scotland by Agricola, and added seven forts to it: a wise and politic prince knew the necessity of it; and consequently infer we, that he as surely repaired the Carsdike navigation, to supply the soldiers with corn, in that northern situation: and I have several reasons to induce me to conclude, he not only did so, but carried it further southward than before, viz. from Peterborough quite to Cambridge; some of which reasons I shall recite in the history of that hero. At present I shall only hint, that his name has ever been affixed to this famous canal, which has never been regarded by writers. It is of utmost importance in the knowledge of Roman antiquity; and it is an affair of such public emolument, as not to be unworthy of the notice of the legislature; where an inland water-carriage is made, for 200 miles in length, from Cambridge to Boroughbridge.