Looks like I figured out what the problem was.  I had 2 terrain mats with global transparancy driven by a function.  I used this because it was used in the tutorial I was following.  However in my scene it caused black holes in the terrain.  So the simple solution is to simply turn it off which is fine by me.  I'm happy with the scene without it on.

Seeing as I'm a technician, you'd think I'd have figured this out in less time.  It was deceiving though because the holes were not very apparant unless rendered at higher quality and at larger sizes.