This condition, unfortunately, is most often found among grains which have thin exines. Those whose exine is ruptured. In practice the break must extend through the ektexine of the grain to be included in this category. The unknown category are grains which are still identifiable, if they were know to the analyst. Indeterminable Include all grains, no matter which of the deteriorated categories it might happen to fall into, which can not be identified due to changes in its appearance from any cause.
Indeterminable grains are generally most abundant in silt deposits.
As a final statement about degradation Cushing mentioned that from his research and observation he found that Populus pollen tended most often to be crumpled rather than broken and that the normal, low recovery of this species in pollen in the fossil record resulted from the analyst's general inability to recognize Populus in its crumpled state. Havinga in 1984 published the results of his 20 year study of pollen preservation in soils. This is one of the most important studies of its kind because of how long it was conducted and checked. Next, he placed a number of these packets into various kinds of soils. All packets were exposed to the elements except the leaf mold which was left in a greenhouse.