the Precambrian and early Paleozoic. The oldest Dalradian rocks (the Grampian Group) were deformed and metamorphosed around 750 Ma. The deposition of younger Dalradian sediments continued until 590 Ma, when the sediments underwent transformation to the greenschist facies during the Proterozoic and Ordovician. Highland Border Ophiolitic Rocks Modeling of gravity and magnetic data along the fault has confirmed the presence of an extensive ophiolite suite. The Dalradian metasedimentary rocks are overlain by an obducted ophiolite that is continuous for at least several kilometres on either side of the Highland Boundary Fault. The models generated from magnetic data suggest that the ophiolite is only slightly displaced vertically by the fault. Old Red Sandstone The Old Red Sandstone is a magnafacies of red beds and lacustrine deposits from the Late Silurian to the Carboniferous. The NE segment of the Highland Boundary Fault is marked by an abrupt change in the dip of the Old Red Sandstone from around 20° to near-vertical and subsequently exposes the Old Red Sandstone basement. Displacement along fault It is currently believed that there were two main displacement events along the Highland Boundary Fault: the Acadian, and the post-Acadian. Evidence for the Acadian displacement event is based on the geochemical study of detrital garnets in the Lower Old Red Sandstone on the Northern limb of the Strathmore Basin. These garnets were linked to those in isolated Dalradian sediments in the northwest, providing evidence for post-Early Devonian (Acadian) movement to be only few tens of kilometers. In addition, the Lintrathen ignimbrite, which is present at the base of the Lower Devonian sequence was traced along the fault and it was found that the displacement was both short and lateral. The post-Acadian movements are highlighted in the stratigraphy of the region. The Lower Old Red Sandstone is unconformably overlain by Upper Old Red Sandstone, where the Upper Old Red Sandstone is tilted close to the Highland Boundary Fault. Red squirrels The boundary is used as a natural barrier to prevent northwards movement of grey squirrels, thus protecting the only red squirrel population in the Highlands. Further reading References Geology of Scotland Silurian geology Devonian geology Seismic faults of the United Kingdom Highlands and Islands of Scotland