The diamond pipes or clusters of pipes at diamond bearing locations attest to this, as do alluvial diamonds in stream sediments associated with impact fields, ie basins which formed during an ancient cometary impact. The Tweed Valley in far Eastern Australia is one such, the diamonds that turn up there the highest quality in Australia, satellite photography has identified large impact basins in Western Australia, including a system of interlocking impact formations, visible on Google Earth, and on nightly TV Weather Maps of Australias mainland. Picture shots of drops falling into milk for instance, a crown like structure will appear, the points on the crown corresponds to the vents formed during impact that carries impacted material, and pieces of the comet, diamonds, to the surface. Typically a diamondiferous crater will have a central peak associated with the impact, see Mount Warning in the Tweed Valley, however the diamondiferous pipes are at the boundaries of the crater. Obtain a GPS and go to the locations you have pinpointed from satellite photos, use an ultra violet light source to find which pebbles and pieces of gravel fluoresce in the UV, then find which stones will leave a scratch mark on glass. The ones that do are the diamonds, I have used this tequnique to locate some great stones from a hitherto unmapped source on Kangaroo Island, off the coast of South Australia. Word is that at the diamond mines in South Africa the diamonds are getting bigger the deeper the miners dig.. tales of boulder sized objects arise, where miners gather to drink and talk, when they get to the nucleus of the comet maybe thousand ton diamonds will be found.