Ill I < 1:1 8SE1 l. 1 Rl V< l. GEOLOGY <H ALASKA. 



menl was observed to I"- southward, as baa been Btated by several other 

 travelers. The coast ran-.- of Alaska was therefore a center of ice accumula- 

 tion during the < llacial epoch. 



A' Limit o) • Uion. — The most northern locality at which glacial 



furrows have been observed along the Yukon is about a mile below the 

 mouth of the L Bowlder day occurs some sixty or seventy miles lower 



down the river and, if of true glacial origin, indicates that the oorth< rn 

 limit of the ancient glacier must have been approximately a little north of 

 latitude 62 . This is the limit assigned by McConnell. More detailed in- 



stigation is needed, however, before the extent of the ancient glacier can 

 l>r definitely assigned. No terminal moraines marking the extent of the ice 

 invasion have been reported, and we are -till ignorant of the disposition <>f 

 the immense amount ot debris thai was removed .from the glaciated area. 

 Neither ha- a divisi fthe period ofglaciation been recognized. 



Terraces. 



Stn vm Terraces along the Yukon. — The first terrace observed in ascending 

 the Yukon is on the right bank of the river, a 1 tout thirty miles below Anvik. 

 At that locality there is a marly perpendicular escarpment about fifty feet 

 high, formed of sand and well-rounded stones that have been deposited 

 against the Bteep mountain Bide. The surface of the gravel <1<] •< .~i t tonus a 



shelf which may be traced for a mile or i c 



act - along this part of the river are ool common, owing, apparently, 

 to their having been removed by the erosion of the Btream. A.bove Anvik 

 they become more and more frequent, but do nol form a conspicuous feature 

 in the landscape until after passing the mouth of the Porcupine and approach- 

 ing the international boundary. 



• M I I rath 'e station, near the international boundary, the elevation 

 of the highest U trace was determined by angulation to be 73 I feet above the 

 river. The terrace at this poinl i- nol Btronglj defined, but that it is a river 



med t ■ certain. Its elevation Beems greater, however, than 



i -• terraces Been either above or below the 1 ll-t meridian. 

 I m tin- boundary all the way up the Yukon to the mouth of the Lewes, 

 and up thi I. to Lake Lindemann, terraces are not only conspicuous 



hut form an importaut element in the Bcenery of the region. 

 'I'le referred to are of two types : I • lake terraces, described 



- in ad and (2 stream terraces. The stream terraces are 



rable into two groups, a rock-cut terraces and I b I gravel terra* i 



nol common along the Yukon, vel a few < spicu- 



ved Their surfaces are usually covered with river- 

 that in - their true gem sis is obscure. \ 



