1. A method for depth correlating a plurality of well logging measurements each comprised of data taken at a plurality of depths within at least one borehole, said method comprising the steps of: deriving a first activity function from a first of said measurements; selecting first data points from said first measurement corresponding in depth to maxima of said first activity function, each of said first data points having magnitudes greater than a preselected first noise level; deriving a second activity function from a second of said measurements; selecting second data points from said second measurement corresponding in depth to maxima of said second activity function, each of said second data points having magnitudes greater than a preselected second noise level; and comparing said first and said second data points.