Summer of 1977 I saw a large oval black object hovering just over the tree tops going very slowly.

In the summer of 1977 as I walked back towards my home from the park in our neighborhood, in a small housing development, I noticed a very large but quiet UFO hovering over the tree tops.  The object captivated me.  I could not take my eyes off it.  
Instead of going home, I followed the UFO as it moved slowly across the tree tops in the wooded area that surrounded the development.  I followed the UFO, for approximately 15 minutes, to Quince Orchard Road, and it continued straight into the woods across the road.  (At the time that area was all wooded).  I could not follow it any further.
The UFO looked oval/dome shaped.  It was very large.  It was dark colored like gray/black.  It had windows along the top dome section.   Not all windows where lit, but there was some light coming from some of the windows. It traveled very slowly, because as I followed it, it stayed ahead of me but I didn’t lose sight of it until it went into another wooded area where there was no road.
I wanted to see if I could continue to follow this thing, so I caught a ride with a car that came along just after losing sight of the UFO- the fellow that stopped to give me a ride said he saw something.  I jumped in and told him I had seen it too, that I had been following it from Quince Orchard development.   He drove a little further to the little shopping center at the end of Quince Orchard Rd. but it was gone.
I don’t know who that fellow was or if he ever reported the sighting.  But I never said anything to anyone about it until I had been married for awhile.  I told my husband and my four children.
I wonder if the occurrence seen in approx June of 1977 was the same sighting I saw!   I think the UFO came from what is now the Seneca Park area.
Witness indicates that the date of the sighting is approximate.  PD