Macadam driveway losing rocks
That doesn't look like asphalt or what you called macadam, it looks like what we call "modified" which is progressively smaller stone chips usually slag or limestone containing a top coating of a fine layer of the same material. After the modified stuff is compacted and weathered and run over with machinery the material resembles an asphalt or loose concrete product that is great for driveways and walkways but will become somewhat loose with age and use.