1 68 ANATOMY OF THE GVMNOSPERMS 



a compact clay, which offers a practically air-tight matrix of 

 essentially the same physical character in all cases. It therefore 

 seems improbable that local variations of the inclosing material 

 could have been so different as to give rise to the diverse aspects 

 of decay noted, though such may have been a factor of secondary 

 importance. The fact that under essentially the same conditions 

 some specimens were well preserved while others were badly 

 decayed, at once directs attention to the probable operation of 

 antecedent causes. It is quite obvious that trees which eventu- 

 ally become fossilized are neither of the same age when they fall 

 nor are they in the same condition of soundness. Some may be 

 quite sound, while others may be infested with fungi, and the living 

 tree may therefore present the somewhat advanced progress of 

 decay. But the fossils of the Don deposits are obviously fragments 

 of trees which had been brought, through the agency of water, to 

 the places where found, and it is quite clear that while some of the 

 trees may have been speedily buried others were no doubt a 

 long time in the water before being inclosed in the sedimentary 

 deposits. Decay would have an opportunity for extended devel- 

 opment under such conditions, and it would even continue for 

 an indefinite period after entombment. On the other hand, the 

 rapid entombment of a vigorous tree in which decay had not 

 yet made its appearance might involve the inhibition of fungoid 

 growth. On this hypothesis, which seems to present the prefer- 

 able alternative, it is possible to satisfactorily account for the 

 varied states of preservation noted, as arising under essentially 

 uniform conditions. 



The common larch (Larix americana) is another wood of very 

 widespread occurrence throughout the Pleistocene deposits. Two 

 widely separated localities may be selected as affording exam- 

 ples of its preservation. At Dahlonega, Georgia, this species has 

 been found in the black clays, which are to be regarded as prob- 

 ably synchronous with and equivalent to the Pleistocene deposits 

 of more northern localities (51). The material was found to be 

 wholly free from impregnation with mineral matter, but it exhib- 

 ited the somewhat extreme effects of advanced decay with the 



