Heavy mineral suites from the Triassic and Jurassic strata in the Vale of Glamorgan were examined and found to consist primarily of zircon, garnet, tourmaline, and rutile. It is thought that the sediments were deposited in an advancing sea bordered by Carboniferous limestone (in places by Old Red sandstone and Millstone Grit) and that material was derived very locally, rather than by transport from inland areas by large rivers. Probably the coast was steeply inclined. Detritus from the Brittany land mass and granite area of southwest England was brought in by offshore currents. In the discussion, it is pointed out that the distribution of garnet varies with horizon rather than shore-line outcrop, and the claim of the small amount of detritus from inland regions is questioned.