The annual layers of sediment deposited in lakes and fiords by meltwater from glaciers. Each layer consists of two parts deposited at different seasons and differing in color and texture so that the layers can be measured and counted. If the series is complete, the number of layers gives the date on which the ground was vacated by the retreating ice. Varves were discovered by G. De Geer at Lake Ragunda in Sweden in 1905, and have since been found in many other regions. They differ in thickness from year to year. These differences were attributed by de Geer to variations of solar radiation and hence are supposed to be similar in all parts of the world. It was proposed that in this way dates of varve series could be determined even if the upper layers were missing, but this method of dating has been doubted.