  The spatial-kinematic structure of 48 young star clusters and associations is
investigated. Moran's $I$ statistic is used to quantify the degree of kinematic
substructure in each region, and the results are compared to those expected
assuming the hierarchical or monolithic models of star cluster formation. Of
the observed regions, 39 are found to have significant kinematic substructure,
such that they are compatible with the hierarchical model and incompatible with
the monolithic model. This includes multiple regions whose $Q$ parameter shows
the region to be centrally concentrated and clustered. The remaining nine are
compatible with both models. From this it is concluded that the kinematic
substructure of the observed star clusters represents strong evidence in favour
the hierarchical model of star cluster formation over the monolithic model.
