Analysis of ecological successions in Upper jurassic hardgrounds at Skorkow (southwestern Holy Cross Mountains), central Poland, made it possible to test the general model of ecological succession proposed by Goldring and Kaźmierczak (1974). An ecological succession is not really evident in calcarenitlc hardgrounds, except when developed on pelletal limestones. This is probably due to the high rate of cementation preventing community maturation. A succession is best developed in calcilutltic hardgrounds. Two additional criteria indicative of substrate consolidation are recognized: mode of oyster attachment and bivalve boring into filled formed crypts. A change from boring to nestling Is recorded in some bivalves. Influence of different hardground-microhabitats on the boring pelecypod associations is recognised