Install R with homebrew under Montain Lion (Mac OS X 10.8.X)

You need to install gfortran before R. 

$ brew install gfortran

You might find that you don't have XQuartx. Please download and install it at https://xquartz.macosforge.org.

$ brew install R
Unsatisfied dependency: XQuartz
Homebrew does not package XQuartz. Installers may be found at:
https://xquartz.macosforge.org
Error: An unsatisfied requirement failed this build.

After you install XQuartz, you can install R like this:

$ brew install R