The logit and probit are different models, and they are interpreted differently.

If you have indeed estimated a probit, and if you have indeed calculated the marginal effects of the variables (not the straight coefficients), and the marginal effect of "log x" is -0.1, then the interpretation is that a 1 unit increase in log(x), which represents a 100% increase in x, reduces P[y=1] by 0.1; that is, a 100% increase in x reduces the probability by 10 percentage points.