Ideally a series consisting of limestone, shale, sandstone, shale, limestone would indicate high water levels diminishing to a shoreline environemnt the rising again to deep water.
Because the range of depths in which shale and limestone can be deposited are quite wide compared to sandstones, frequently the water never becomes shallow enough in a given location for a shoreline environmet to exist. In these instances a series of alternating shales and limestones are observed.
In the diagram below, two complete cycles are shown. From the bottom - a deep water limestone facies gives way to shallow shale deposits. Water levels were low enough for the developemt of a nearshore sandstone to develope. This became submerged again and shales were again emplaced, followed by limestone as the sea level continued to rise. The cycle continued again above without the appearance of the sand unit.