Beating or walking the bounds is an ancient practice that would be performed by clergy and parishioners together with a group of local boys.
The boys would be escorted along the boundary, and beat with willow sticks any markers or natural features along the boundary, for the purpose of memorising the jurisdiction of the Parish boundary.
This custom usually took place on Rogation Sunday or Ascension Day, but not necessarily in every year, this custom is still practised occasionally by enthusiastic groups in some parts of modern England.

Where are the boundaries of Lower Gornal Parish?

I will try and define by description, but will only make sense if you are really familiar with the area or look at old maps.

The Parish of Lower Gornal bounds are roughly defined:-

By starting at Bobs (Straights) Brook on the Western boundary near Cotwall End and following South to Askew Bridge and Coppice Mill near the 'Crooked House'.
From there on the Southern boundary by a small water course which runs south of the Himley Road and along the old mineral railway walk at the back of the Forge Inn to Hunt's Mill on Coopers Bank Road.
Thence northwards as the crow flies, across Milking Bank to the top end of Grosvenor Road near the new Meadow Lark Inn, following across the old Gibbons works, now 'Black Country Forrestation' and thence to the Junction of Jews Lane with Robert Street.
From this point across Cricket Meadow to where Holloway Street joins Vale Street at Ruiton, then across the fields to the starting point at the North end of Bobs Brook whence started from.

Some of the boundary may now be inaccessible due to modern development.