62 W. R. Jillson — Recent Yolcaiiic Erujption. 



Of first significance then, and in line with the arguments of 

 Diller and suggestions of Coville, was the discovery in the 

 same locality from which the Yale cast was taken, of the 

 decayed and disintegrating remains of a small tree trunk. The 

 material lay in the bottom of one of the horizontal casts and 

 extended back into it for several feet at least. A portion of 

 this residue, which consisted mainly of broken, powdered 

 charcoal and a small amount of the decayed wood, was col- 

 lected but, unfortunately, was lost in packing out of the 

 mountains. 



In consideration of the fact that the temperatures of most 

 fluid lavas are greatly in excess of the ignition point of wood, 

 it is realized that any carbonized log producing a lava-cast 

 would have a very slight chance of being preserved, even to 

 the end of the period of volcanic activity, unless completely 

 imbedded within the lava. In such an event the log would be 

 reduced to absolute charcoal, but the chances of its discovery 

 in recent, uneroded lavas would be slight. It is thought that 

 the only possible means by which original spontaneous combus- 

 tion eould have been stopped, thus preserving the charred logs 

 in the moulds, would be by the introduction of a completely 

 encasing water jacket immediately following the contact of 

 the lava with the wood. It may be noted again that the casts 

 herein described occur in a considerable depression which 

 might well have been a small collecting basin for the hot and 

 rapidly vaporizing surficial waters which commonh^ accom- 

 pany volcanic disturbances of this kind. The rough terracing 

 of the lava seems to indicate the existence of a rising and 

 widening water barrier and the spur described above is favor- 

 ably situated for directing surface water into a depression at 

 its base. 



The woody material taken from the lava casts has received 

 only superficial examination. The writer, therefore, considers 

 it inadvisable at this time to enter into further abstract con- 

 siderations. If new collections and detailed studies show that 

 this decaying woody residue was a part of the original cast- 

 producing log, and not, as has been suggested, foreign material 

 introduced in some way into the case, the views of Coville and 

 Diller regarding the recency of volcanic activity in the Cas- 

 cades receive direct support. These facts, exclusive of much 

 existing corroborative documentary evidence, would be suffi- 

 cient to establish the occurrence of mild extrusive volcauics at 

 Mt. St. Helens well within the last century. 



Yale Universitv, New Haven, Conn. 



