I come from melbourne and now live in Europe. En tous cas and (at least) European clay are 2 quite different surfaces. yes - you slide on both of them, but the playing characteristics are not all that similar.
In Australia, a lot of courts are referred to as 'clay' when they aren't. I wouldn't be surprised if Evonne Cawley grew up on crushed termite mounds - a popular 'clay' surface in the country areas. Perhaps technically en tous cas is a clay surface, but it doesn't really behave the same way as the stuff here in Europe.