QUATERNARY FORMATIONS - THE DRIFT. 211 



greater tlian the accumulation during the period that they existed as 

 lakes. 



Aside from the accumulation of peat in these extinct lakes, deposits, 

 arising in similar ways, took place in wet localities in connection with 

 'running streams, or in wet valleys, that bear no evidence of having 

 once been lakes. 



Bearing in mind the method of formation, it will readily be antici- 

 pated that great variety in the character of the peat will be the result. 

 Its degree of decomposition ranges from merely dead vegetation to 

 that which has become thoroughly disintegrated, and the value of any 

 given deposit will depend in part upon its character in this respect, 

 since the fibrous condition of peat is one of the serious obstacles to its 

 profitable utilization. It will also be readily understood from its 

 mode of origin, how impurities may become incorporated with it. On 

 the margin of the marsh, the wash from the adjacent uplands will nat- 

 urally introduce more or less of earth or sand. Near the bottom of 

 the bog, earth will naturally become incorporated with the peat, and 

 in those cases where the surrounding regions have in recent times 

 been cultivated, the uniisual amount of earth carried down by tho 

 waters will render the entire surface of the peat more or less impure. 

 That portion of the peat which accumulated while the lake was grad- 

 ually becoming drained to a marsh is more or less filled with the 

 shells of snails, and the remains of other animals that inhabited the 

 lake. In many cases the amount of accumulation of this kind is very 

 considerable, sometimes equaling and occasionally surpassing the ac- 

 cumulation of the peat itself, forming a mixture of marl and peat 

 that will prove very serviceable as a fertilizer. Where the peat accu- 

 mulated in the vicinity of running streams, their periodical overflow 

 has contaminated the deposit in a greater or less degree. A fourth 

 source of impurity arises from travertine, or calcareous tufa, deposited 

 from springs. This, while it is detrimental to peat as fuel, enhances 

 its value as a fertilizer. Hence, in the selection of peat marshes, 

 those which have been, from their situation and nature, sheltered from 

 these sources of impurity, will, to that extent, be favorable to a pure 

 deposit. The situation and the nature of the marsh will also furnish 

 some indication as to the abundant presence or comparative absence _ 

 of the acids which interfere with the direct use of peat as a fertilizer. 

 The character of the vegetation growing upon the bog will, however, 

 be a more reliable indication of this. The presence of shells or marl 

 may be taken as satisfactory evidence of the absence of any harmful 

 quantity of thes6 acids. The number of deposits of peat within this 

 portion of the state is very great, and their purity ranges through all 

 Wis. Sue. — 16 



