R help - Nov 2006 - posterior probability formula in predict.lda

IHi all,
 have a dataset with rows as plots and environmental data as columns.
I have predicted the values using the following

ed.pred<-predict(lda.ed,ed) #lda.ed the model, ed the env. variables
used for the prediction plots

I am wanting to know the formula used by predict.lda for calculating
the posterior probabilities.

Can anyone point me in the right direction?

Thanks