68 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

another. Likewise distinct changes in the character of the clay may occur from place to place in the same bed.
 There are several forms of sedimentary clay deposits based upon the conditions of sedimentation. The following with the exception of the last two, glacial and aeolian clays, are all found in Florida.
 Marine Clays-Fresh water in rivers, etc., may contain much clay substance, consisting of the very finest and lightest particles, which it carries in suspension. This acts as a solution of clay in water. When this fresh water becomes mixed with sea water the clay flocculates and is deposited on the sea floor, or, as is frequently the case, in estuaries or lagoons along the coast. Extensive clay deposits are frequently thus found.
 Flood-Plain Clays-Streams carrying clay material in suspension or rolling it along on the stream floor often deposit much of it in the adjacent lowlands during periods of flood. Subsequent overflows deposit additional layers. Extensive flood-plain deposits are often formed in this manner along the larger streams and in their deltas. Flood-plain clays are extremely variable in their nature and are often calcareous or sandy.
 Lacustrine Clays-Clay material carried by streams into lakes or ponds gradually settles to the bottom of the quiet water to form a deposit of clay on the lake floor. Such clays may be of great purity or they may be mixed with a great amount of.sand or other impurities.
 Glacial Clays-These are sometimes termed till or bowlder clay. These are deposits, which are of heterogeneous character and usually impure, formed by the grinding of rocks or rock fragments by glacial action and deposited by the ice as it me'te:l or by the resulting water in the redeposition of the material. Deposits of this type are only found in glaciated regions. None exist in Florida.
 Aeolian Clays-Deposits of clay formed by the ac ion of the wind are termed aeolian clays. In arid regions clay in the form of dust is blown about and sometimes accumulates in extensive beds. Some less clays are believed to have been deposited in this manner. No such clays are known in Florida.