Out and about with Eric Robinson/A bonus from the enlarged community

摘要

The Tyne at Newcastle in north east England has always fascinated the visitor, its bridges crossing the river where it flows through a veritable gorge. Until recently, there were four (Fig. 3); now there are six including two new additions. Some are 'high level', others 'low', down at river bank. At either level, they are tackling some quite tricky engineering in different ways. Missing from the series, even in known position, is the Roman bridge which is certainly one of the set if only through the Roman name for Newcastle - Pans Aelii. In all probability, it would have been close to the surviving cluster if only because they sit close to the best bridging point, with solid rock banks exposing massive sandstones of the Middle Coal Measures as well as outcrops of some of the richest coal seams worked from adits both up and downstream. Abutments on either bank were simply a matter of keying into one or other of the main sandstone 'posts'. Given the width or the span needed to clear the river, however, the problem arose of the uncertain bed of the river. The Tyne Gorge is really an overdeepened channel to a major river adjusting to a rise and fall of Pleistocene sea levels. The inheritance of this is an erratic rock channel filled with fluid mud. It is one of the successes of the High Level Bridge of Robert Stephenson (1842) that it managed to sink supporting piers to the lofty box span avoiding that channel with its problems. As it is, it has to be one of the wonders of the early railways for the ingenious combination of road and rail in a double-decker relationship, the railway being on top and the road contained in the iron box below (Fig. 4).