The same interesting observations can be made here as indicated previously here. Open the layer package in ArcMap, re-order the table of contents alphabetically like so to show the map better, and this may be a more legible surficial geology legend. Turn off the Culture and Derived group layers, turn on the Raster group layer, and zoom to the layer: 1877 Cambs. Surficial Geology. The scanned map has 50% transparency, but you can use the Swipe function (Effects submenu) to compare it to the underlying web canvas.
The scanned 1877 surficial geology fits quite well with the current web canvas of same. The clay-silt /peat transition to the north and the gravel river beds to the south match well, as do the clay to the north and south-east. But the central region has seen a significant expanse of chalk over clay to the west and reduction of peat in the centre. These reflect not only thre past reduction of peatlands reported by Darby, but also the current change over from greenfield (un-developed) to brownfield (re-developed) lands. The urbanisation can be seen on the Change Matters website by selecting CB4, which takes you to Cambridge UK. North of Cambridge, purple for loss of vegetation reflects that transition.