44 THE ROYAL SOCIETY OF CANADA 



In the narrow gulches tributary to the main valleys, the muck 

 is often very deep, having been formed by bog masses growing in the 

 gulches themselves supplemented by vegetable debris washed down 

 from the adjoining hills. In Lovett Gulch, a tributary of Bonanza 

 Creek, it was found to be 100 feet deep. 



The process of deposition of vegetable material, as above outlined, 

 combining the growth of mosses, and the transportation of forest 

 debris, went on from year to year, and from century to century, and 

 built up those beds of muck, which now contain fragments or remnants 

 of all the vegetable growth of that vicinity throughout the period of 

 their formation. The plant history of the Klondike district for the 

 "Muck" Period, which extends from the beginning of refrigeration 

 in Pleistocene times to the present, is therefore included and recorded 

 in these beds. 



On wetter portions of sloping hillsides, bogs, composed of mosses of 

 several kinds, occur, but in these bogs there is little evidence of the 

 presence of transported material such as composes a large part of 

 •the muck of the valleys. In fact they are very similar to the bogs 

 in Manitoba and other western Provinces of Canada, though undoubt- 

 edly much older, for the bogs of Manitoba are definitel}'^ post-Glacial 

 since they began their growth after the last continental glacier retired 

 from the country. In these hillside bogs sheets of clear ice are fairly 

 abundant, and occupy various attitudes from vertical to horizontal, 

 but as far as my experience and observations went, the horizontal 

 attitude was not as prevalent as in the muck of the valley bottoms. 

 The explanation of this appeared to be that the muck, being stratified, 

 broke readily in horizontal layers under the hydraulic pressure of 

 spring water rising through it from below, while the higher bogs, 

 being unstratified, did not break in any such regular way. 



On the upper terraces of Bonanza and Hunker Creeks, which 

 are underlain by the White Channel Gravels, bogs are either absent, 

 or are not very extensively or strongly developed, and where present 

 are composed of moss like those of the hillsides just described. 



On the lower terraces of Bonanza Creek, which were about 30 feet 

 above the bottom of the valley, there were beds of bog or muck over- 

 lying the gravel, but unfortunately I have no detailed record of their 

 character. 



We have thus seen that a period of great cold set in when the 

 muck began to form over the gravel flats in the bottoms of the present 

 xalleys, and the question naturally arises whether the perennial frost 

 which entered and cemented the ground at that time has remained 

 in it up to the present time. This question must evidently be answered 

 in the affirmative, for if the frost had left the ground, the supply of 



