  The aim of the present work is the construction of a mass-selected galaxy
cluster sample based on weak gravitational lensing methods. This sample will be
subject to spectroscopic follow-up observations.
  We apply the mass aperture statistics and a derivative of it to 19 square
degrees of high quality, single colour wide field imaging data obtained with
the WFI@MPG/ESO 2.2m telescope. For the statistics a family of filter functions
is used that approximates the expected tangential radial shear profile and thus
allows for the efficient detection of mass concentrations.
  We identify 158 possible mass concentrations. This is the first time that
such a large and blindly selected sample is published. 72 of the detections are
associated with concentrations of bright galaxies. For about 22 of those we
found spectra in the literature, indicating or proving that the galaxies seen
are indeed spatially concentrated. 15 of those were previously known to be
clusters or have meanwhile been secured as such. We currently follow-up a
larger number of them spectroscopically to obtain deeper insight into their
physical properties. The remaining 55% of the possible mass concentrations
found are not associated with any optical light, or could not be classified
unambiguously. We show that those "dark" detections are to a significant degree
due to noise, and appear preferentially in shallow data.
