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We present Submillimeter Array (SMA) observations of seven massive molecularclumps which are dark in the far-infrared for wavelengths up to 70 $\mu$m. Our1.3 mm continuum images reveal 44 dense cores, with gas masses ranging from 1.4to 77.1 M$_{\odot}$. Twenty-nine dense cores have masses greater than 8M$_{\odot}$ and the other fifteen dense cores have masses between 1.4 and 7.5M$_{\odot}$. Assuming the core density follows a power-law in radius $\rho\propto r^{-b}$, the index $b$ is found to be between 0.6 and 2.1 with a meanvalue of 1.3. The virial analysis reveals that the dense cores are not invirial equilibrium. CO outflow emission was detected toward 6 out of 7molecular clumps and associated with 17 dense cores. For five of these cores,CO emissions appear to have line-wings at velocities of greater than 30 kms$^{-1}$ with respect to the source systemic velocity, which indicates thatmost of the clumps harbor protostars and thus are not quiescent in starformation. The estimated outflow timescale increase with core mass, whichlikely indicates that massive cores have longer accretion timescale than thatof the less massive ones. The fragmentation analysis shows that the mass oflow-mass and massive cores are roughly consistent with thermal and turbulentJeans masses, respectively.

Formation of Massive Protostellar Clusters -- Observations of Massive 70 $\mu$m Dark Molecular Clouds