You mixed 2 Basic Textures(*.brt) to create a new combined Material. Usually you would save the result as Jade mentioned if you want to reuse it. I suspect you didn't save it to the Material Library and therefore can't find it now.


If you hold down Shift and click on the name LowSmog 16 (in your example) you will see all the basic component textures available.
When you modify one and want to keep it you can add it to the Textures library by clicking Add at the bottom left of the window which opens.[shown at item 9 in table of contents]
You're confusing Textures with Preset Materials > Materials are made from Basic Textures.