Abundances of magnetic spherules in Jurassic cherts from the Austrian Alps are compared with abundances in Silurian and Permian salt samples. Constancy of spherule influx is probable and rate of deposition of salt can be reasonably estimated. Consequently, it is possible to calculate rate of chert deposition. For three samples the probable range is one cm/100 year to one cm/400 year. This is generally in accord with stratigraphically determined rates if it is assumed that chert-shale couples were rhythmically deposited with shale deposition being much slower than that for chert.