Your working on some displacements created using a single brush and things are going fine. Here's a single brush. Let me displace the front and top faces. Lookin' good but - hold on - I want to add another displacement to the face at one end of brush. "Simple. Just add another brush at the end and displace it." NO SIR. We shall use voodoo magic that allows use to add more displacements to our already displaced brush without destroying anything! Simply click this little bugger dispmask in the top toolbar and it'll show any non-displaced faces on our brush! Select it, displace it, do whatever you will and voila!