From aerial photos, the earthworks appear to be square shaped, although inspection from the ground shows them to be nearly circular in shape, about four feet high, with a slightly dished interior, dipping to around one foot below the rim. Various internet sources mention a cross wall, or masonry...although when I visited, only a few stones were visible on the Northern edges of the earthworks.
One interesting fact about this field though, is that the ordnance survey map shows the course of the old Roman road running North South through this field. If the route marked on the map is to be trusted, the old Roman road would have run just a few feet from the Eastern exterior of these earthworks....indeed, the profile of the field shows a distinct mound of earth (an agger) running the full North South length of it, clearly indicating where the road would have run. There is a slight depression between the Roman road and the earthworks. An 1863 map of Westmorland, clearly shows the earthworks next to the route of the Roman Road, and they are labelled as a Roman Fortress, so it's looking more and more unlikely that these remains represent a motte and bailey castle or medieval ring work.