and turns sharply left onto the till. It used to go straight on and pass the north front of Grimsthorpe Castle. When the soil in the field beyond the bend is bare, its course can still be seen. The castle's owner did a deal with the turnpike trustees. He brought land on the other side of the road into his park and built them a new, though longer road around it. Once the semi-circular diversion is completed, the road turns sharp left again, through Grimsthorpe where it is on Jurassic clay. The 1824 Ordnance Survey map shows both the old and the new roads. At Grimsthorpe village, the A151 is in the second of the main valleys dissecting the plateau, that of the East Glen river. From its association with Edenham, this river is often called the Eden. The West and East Glens join near Wilsthorpe, at . Through Grimsthorpe and Edenham, there are numerous bends and winds across the small exposures Jurassic soils, glacial gravel and alluvium, until the road climbs out of the valley over the till-capped ridge which separates Edenham parish from Bourne. On the glacial clay soil of the till, it passes between woods, including Bourne Wood. Bourne As the road arrives back on the Jurassic clay, it meets the A6121, a road designation which ends here, having begun at Morcott, in Rutland, on the other side of the A1, hence its beginning with the digit 6. In 1824, there was a toll gate here. The course of the A151 is directly down the slope into Bourne. It is clear archaeologically that the road used to run parallel with this and about 200 metres to the south. Historically, there appears to be no commonly available record as to when the move was made. It was certainly in two stages. The move of the upper part was probably made in the 18th century; the lower, in about 1140, when Bourne castle was built across it. Its present course is dictated by the former presence of Bourne Castle at the town end and by a desire to keep to the crest of a slight ridge in the hillside. It is towards the top of this section that it is possible to detect a change in slope betraying the former presence of a shore of the Devensian periglacial lake, which was impounded by the ice into the Fenland basin.