The objective was to determine to what extent geology, mainly structure, influenced blasting practices and results in limestone and dolomite quarries, and to ascertain how geologic features could be utilized to advantage in quarrying. The rock in the quarries visited was mined by bench blasting with long cylindrical charges in vertical boreholes. The gross geologic features observed to influence blasting are: horizontal bedding without conspicuous jointing, horizontal bedding with conspicuous jointing, and folds, faults, unconformities, caves, and filled joints. As an example of how geology affects blasting, horizontal bedding with conspicuous jointing provided a condition where ammonium nitrate-fuel oil, AN-FO, misfired. The following reasons for the misfire are possible: (1) when poured into the borehole, the AN-FO was lost into open joints and bedding; (2) water migrating along joint and bedding planes intersecting boreholes desensitized the AN-FO because the blasting agent was not loaded into a plastic sleeve; (3) the undetonated explosive column in the borehole was cut off by rock shifting along bedding and joint planes. This shifting is caused by rock stresses produced by earlier detonation of nearby charges. A first step in planning a blast design is to identify the geologic features such as those mentioned above. The quarry officials attempt to adjust blasting techniques to minimize detrimental geologic effects and maximize beneficial geologic effects.