THE DATE OF THE GLACIAL PERIOD: 597 



tries, the average production of compact matter may in a 

 general way be estimated at one foot in a century. 



In immerged logs, formed of vegetable debris falling into 

 water, the peat grows more slowly and less regularly. The 

 actual rate of its growth has not yet been positively recorded. 

 In very extensive bogs, stretching between Swiss lakes, timber 

 posts have been discovered on the line of an old road, and 

 parts of a bridge buried beneath five or six feet of compact, 

 black peat. Although the exact date of these constructions 

 has not been fixed, the discovery of Roman medals in the 

 vicinity suggests the beginning of the Christian era. This 

 shows that the kind of peat which results from the maceration 

 of plants under water is of much slower growth than the peat 

 layers of the emerged bogs. It is also more compact, and is 

 quite black, the vegetable matter being more completely de- 

 composed, and its internal structure generally so destroyed as 

 to be unrecognizable. The peat of emerged bogs, on the con- 

 trary, is yellowish-brown, fibrous, its annual layers distinct, 

 and the woody fragments more generally recognizable. 



Since the above was written a well sunk at Germantown 

 through the till 100 feet deep, nearly a mile northeast of the 

 exposure shown on p. 593, penetrated a peat layer several 

 feet in thickness, showing that the deposit is extensive and 

 perhaps older than we had estimated. It should also be said 

 that Mr. Leverett is not fully convinced that the gravel under- 

 neath the peat is glacial, but thinks that it probably is. 



But we are not compelled to assume a slow growth, nor 

 even the average growth as the rate. The cool, moist climate of 

 a glacial age would seem to be peculiarly favorable to both 

 the growth and the preservation of peat ; so that two hun- 

 dred or three hundred years is perhaps ample for the pro- 

 duction of all the facts connected with the peat accumula- 

 tions at this point. If it be asked how such a deposit of 

 peat could be overwhelmed with ice without disturbance, the 

 answer is that, as suggested by N. IT. Winchell, before che 

 reinvasion of ice the peat in the kettle-hole and probably the 



