my gravel driveway seems to be turning into concrete?

I'm not sure if this is concrete or not but my soil is mostly clay and after I finished killing all the weeds that had made my gravel driveway look like a most unkempt lawn I've realized now that most of the gravel seems to have sunken down into the earth and when I try and dig it up I am seeing chunks of what looks like concrete. I'm at a standstill at what to do at this point. The driveway is large and circular and the cost of the gravel upon building the house was around 3 grand. I choose...

my gravel driveway seems to be turning into concrete?