Hudson's model Nichols (1989) of the elastic properties of fractured rocks is based on an equation for the mean field in a solid with a random distribution of inclusions. We consider Hudson's model only to first order in crack density of penny-shaped cracks. This is equivalent to only allowing single scattering and ignoring crack/crack interactions. For this approximation to hold, the crack density must be low. Hudson's formalism can be directly presented in S&M group formalism.