[R] Applying function to elements of matrices in a list

[statmobile]

Hello R-help,

Please cc me on all responses, as I only receive summary emails from 
this list.

I'm wondering if anybody has any tips on how to accomplish this 
efficiently.  I have a list of matrices, and I'm trying to get the mean 
of the [i,j]'th element of each matrix in a list.

So if I have a list of matrices, say

x <- list(a=matrix(rnorm(4),nrow=2),b=matrix(rnorm(4),nrow=2))

How would I get a 2x2 matrix, where the i,j'th element would be the mean 
across the the list of each of the i,j'th elements in the list?  That 
is, where the [1,2] element would be the average of a[1,2] and b[1,2].

Of course my list and matrices are much larger, and I was hoping there 
would be some trick with lapply that I may be missing here.

Thanks,
Brian