JimmyJames,
I believe that gravitational fields are composed of matter that contains more energy than space but less energy than solid matter. When two gravitational particles meet, they tend to form one particle, thereby collapsing space. This effect is known as gravity. So in other words, gravitational fields do not have enough energy to be physical. And when they do have enough energy to be physical, they are no longer called gravitational fields; the are called matter.
Tom