One of Dran's magical innovations. It is a small marble made of black glass stuck somewhere between liquid and solid and it functions as a form of storage. A large amount of matter can be compressed into weightless light and held inside this marble and reconstituted whenever the time is right. Travellers use deep marbles to store items such as clothes, weapons, and other bagage. The marble can be safely stored in ones pocket or backpack. The only problem with such a miracle is that since it is so very small and easy to carry, it might slip ones grasp and be lost forever.
Other applications include fuel storage for certain machines.
They are incredibly expensive for their size, and are commonly sold by merchants.