The invention is provides a method of logging rock core. A digital photograph of core from a borehole is taken and the image is first processed. This involves calibration and correction, or un-distortion, of the digital image. A reference frame is included in the photograph to facilitate processing. The two-dimensional image is then used as a virtual three-dimensional model of the core enabling length and angle measurements to be logged. These include linear rock interval measurements as well as angular measurements of geological structures. The method is implemented using a software program which enables suitable hardware. The software program will be provided on a suitable computer readable medium. Manually logged data of the same kind is imported for comparison to data logged using the software program. All of this data can be displayed on the image and incrementally on a Stereonet as it is logged. A permanent visual record and reliable means of rapidly assessing the accuracy and quality of the data is provided. The invention also provides for automation of a significant part of the image processing and logging. The reference frame is preferably provided by a rock core tray frame having suitable indicators with known dimensions. The frame is rectangular with orthogonal lines on an upper surface. The mid-points of these lines are marked and spaced apart brackets provide for elevated lines superimposed on the orthogonal lines.