York Archaeological Trust
The proposed development lies on gently sloping ground on the northern bank of the River Foss up-river from Foss Bridge. It is evident from the height of the modern river frontage that the ground level on the north bank has been raised considerably. The present course of the River Foss is the result of canalisation in the late 18th century. The modern ground surface appears to slope gradually down from north-east to south-west between Dundas Street and Garden Place. The highest point within the development area is approximately 11.25m Above Ordnance Datum (AOD) at the north-eastern end of Dundas Street; the lowest point is at 8.8m AOD in Carmelite Street.
The geological history of York is a complex one. The solid geology is Bunter and Keuper Sandstone (Geological Survey of Great Britain (England and Wales) Sheet 63 1967) laid down during the Triassic period, some 225 million years ago (Warrington 1974). Over this lies a complex drift geology of Warp and Lacustrine clays which formed during the last glacial inundation, when the vale of York was a glacial lake. The development area lies on the north-east edge of a promontory of boulder clay between the Rivers Foss and Ouse which formed during the last glaciation in the vale. This promontory was used as a naturally defensible site by the Romans. To the east of the boulder clay peri-glacial and post-glacial alluvial silts and clays form a thick band of deposits laid down in the many inter-cutting channels of the River Foss. The prediction of exactly which of the underlying geological deposits will be found in any particular part of the development site is thus difficult to define with precision. The uncertain course of the River Foss in pre-Norman times and the likelihood of encountering over-bank deposits which seal archaeological material render precise predictions about the depth and nature of the archaeology of the area difficult without further investigation.