Massive, low flying, slowly moving craft that emitted no sound.

While travelling a back road through a wooded residential area, I observed a very large object in the sky that appeared to be just above the tree tops.  I slowed my car to a near stop.  My impression was that it was massive; football field in size.  I could almost sense its mass before seeing it. 
It moved extemely slow, there was no sound.  There were lights,but I can no longer remember if colored or white nor the configuration. The lights were not exrememly bright.  Its color was dark and shape unknown because of tree cover. 
I could not clearly see its details, only a partial outline and impression of tremendous mass.  I was perplexed and frightened. 
I was following a friends car. When we reached our destination, her first words to me, unprovoked,were "Did you see that?"  We were stunned. 
I remain stunned to this day.
Witness indicates that the date of the incident is approximate.  PD