Dirac's Large Numbers theory requires the creation of new matter, either in special places (such as the centres of galaxies) or everywhere in the Universe. A special difficulty which he encountered with this prediction was the effect of uniform creation on the structure of old rocks. It is now shown that this difficulty can be removed if what is involved is the creation of interstitial atoms. These, it is known, are trapped on sinks such as dislocations and so produce no cumulative disruption of the crystal structure. It is suggested that, in consequence, the dislocation density of rock may increase perceptibly with its age.