19 1 7] FORSAITII—ALLOCTHOXOUS PEAT 190 



apparent that this peat, a very common type in the Florida lake 

 region, is not, as is ordinarily supposed, of autocthonous derivation; 

 but, on the contrary, is almost entirely allocthonous. It would 

 thus appear that the development of this form of deposit is in 

 accord with the general principle of sedimentation for peat and 



f coal in general. 



One of the most interesting phenomena in relation to the forma- 

 tion of peat beds is that illustrated by completely or nearly filled 

 lakes. As has previously been stated, there are several distinct 

 steps in the process, beginning with an open lake surrounded by 

 sandy shores, of which condition Lake Weir served as an example. 

 The next is seen where the herbaceous zone has crept in from the 

 shores, as illustrated by the "saw grass" marshes around Lake 

 Harris. The third stage is the conversion into a bog as a result 

 of drainage and the introduction of woody plants, which marks the 

 end of the process. Consequently, the value of this last formation 

 as a peat builder has in all probability been overestimated, since 

 the detritus formed by it directly comprises but a small proportion 

 of the whole, especially in the more tropical areas where perpetual 

 exposure is favorable to destructive activities. A series of samples 

 from one of these beds, if studied only superficially, shows two 



ma 



mat of fallen plants and roots, and the lower layer consisting of a 

 somewhat homogeneous mass of minute debris. This older plastic 

 material is believed by many w r riters to have resulted from a more 

 prolonged period of reduction of detritus similar to that found in the 

 upper part of the bed. This conclusion, derived from gross 

 examinations alone, is nevertheless misleading, and on this account 

 it seems advisable to refer to microscopic investigations. A bog 

 near Leesburg will serve to illustrate. A topographical study of this 

 area showed that it was at one time either an arm of Lake Harris 

 or a connecting link between Lake Harris and Lake Griffin. At 

 the present time the filling processes have reached completion, and 

 the entire area is now dry land bearing a dense forest of coniferous 

 and deciduous trees. Probings in several localities showed about 

 15 ft. of peat resting upon a stratum of bluish clay (the initial stage 

 of "fire clays" usually found under coal beds). Above this lamina 



