Are there any plants above it that might have a scale or aphid infestation?

A picture would be most helpful.

To gargwarb:
There are no plants other than these creeping phlox.
To rhizo:
I will add a picture....not sure how to do it at this point.
I am also including the following as it appears to have some bearing on the problem. The ground was prepared by using a layer of topsoil, on top of that a layer of mushroom compost, and then another layer of topsoil. I have used a spray fungicide (Chlorothalonil) that seems to be helping, but it has rained within a few hours of application each of two times. There are very thin mushrooms coming up like crazy and many of them have this substance on them, even within 12 hours of their appearance. Where they are coming up in the phlox, the black gooey substance seems to then be growing in that area where the mushrooms came up, especially if the mushrooms had the substance on them to begin with.
Hope the picture and this other information might help.
Cliff

rhizo: there is a picture that was just posted (new post) showing the black affected area as best as I could show it.

Your image is here
http://forums.gardenweb.com/forums/load/pests/msg0512294931198.html

Here is a link that might be useful: image