  From muon spin relaxation spectroscopy experiments, we show that the sharp
peak (lambda type anomaly) detected by specific heat measurements at 54 mK for
the ytterbium gallium garnet compound, Yb3Ga5O12, does not correspond to the
onset of a magnetic phase transition, but to a pronounced building up of
dynamical magnetic pair-correlations. Beside the lambda anomaly, a broad hump
is observed at higher temperature in the specific heat of this garnet and other
geometrically frustrated compounds. Comparing with other frustrated magnetic
systems we infer that a ground state with long-range order is reached only when
at least 1/4-1/3 of the magnetic entropy is released at the lambda transition.
