[DB 1506 (3)] Although it is true that many geological deposits can be laid down quickly, there are many which cannot. The majority of deposits still require long ages of deposition. Sand dune deposits, evaporites, and varved sediments are just a few examples. Furthermore, the common occurrence of "angular unconformities" demonstrates that the deposition of the geologic column could not have been continuous. Angular unconformities occur when strata are tilted with respect to each other, rather than lying horizontally one on top of the other. This is generally caused by tectonic processes tilting the lower layers before the higher layers were deposited, and a sharp angular unconformity proves that no deposition was going on while the tilting occurred; thus the deposition has not been continuous.