l62 



SCIENCE. 



[Vol. XX. No. 502 



ahvays so constituted further investigation should determine. As 

 it is comparatively immense, its examination is not so diflScult as 

 is that of the suialler Amccba. the study of which, with this spe- 

 cial object in view, would demand greater care and an eye trained 

 by practice over the microscopically minute. The subject and the 

 facts are important by reason of their bearings upon the minute 

 examination of objects that may, perhaps, possess a more utili- 

 tarian purpose than either the common Amoeba or the almost 

 ei]ually common Pelomyxa. 



The examination in this case was made veith Bausch & Lomb's 

 homogeneous immersion one-eighth, Reichert's oil-immersion 

 one-twelfth, N. A. 1.40, and Gundlach's homogeneous-immersion 

 one-twentieth, N. A. 1.30. 



Treuton, New Jersey. 



GLACIATION IN WESTERN MONTANA. 



BY HERBERT. R. WOOD. 



The evidences of glaciation in western Montana are very ap- 

 parent from Helena to Hope (Idaho). They are shown by a series of 

 parallel valleys with a north and south trend, and another series of 

 rounded oblong isolated valleys, connected by narrow necks of land 

 along river bottoms between mountain chains. The former follows 

 the strike of the rocks, occurring along contact lines, synclinal 

 folds, shore or marginal beds of the Sub-Carboniferous formations ; 

 the others cross the strike, and, like the former, are also largely 

 Ihe result of pre-glacial denuding forces. The direct evidences 

 are erratic blocks, terminal moraines (frequently holding back 

 lakes), clays, strise, gravels, etc. The main range of the Rockies 

 (5,550 feet, at MuUan, above the sea), consisting of Devonian, Car- 

 boniferous and Sub-Carboniferous, has a valley on the west in 

 the upper Cambrian. Further north west the glacial striae run 45° 

 north of vvest, the general course of valley being aO" north of west. 



The elevation at the boundary here is 4,000 feet above the sea; 

 100 miles south of this it is 3,200 feet, in vicinity of Missoula. 

 From the summit of the main range, as given above, to Hope. 

 Idaho, 300 miles, the fall is over 3,000 feet (5,550 — 2,200). The fall 

 from the boundary is not constant ; at Libby, near Idaho, the height 

 is 3,000 feet, forty miles south of this it is 3,500 feet. While the 

 glacial action has been generally from the north, at 100 or 150 

 miles from the boundary seems to have been the end of the ter- 

 minal moraines ; and a series of glaciers came from the south — 

 the higher elevations of the Bitter Root Range. The great Flat- 

 head Valley, which lies west of 114° and extends south from the 

 boundary for 150 miles to Ravalli, is about 80 miles wide. In its 

 southern portion a lake is situated, which is about 35 miles long, 

 dammed by a terminal moraine 300 feet high. The lake is 1,000 

 feet in depth, its northern shore being a plain, extending for 30 

 miles, representing an old lakebei. Another moraine extends 

 across the northern part of this plain, making the boundary line 

 of its northern shore. Such a glacier that could produce this 

 excavation must have- been 2,000 feet in thickness and 25 miles 

 wide. Heavy beds of clays, 150 feet in thickness, cover the plain, 

 with a few boulders and thin beds of sand in its lower layers, 

 which is followed by gravels. The worn-down roots of a moun- 

 tain range are noticeable at both the north and south shores 

 of the lake. This valley runs along the shore line of the lower 

 Cambrian quartzitic series. Some glaciated valleys enter this from 

 the west. The direction of this great glacier seems to have been 

 south-east, crossing a range of mountains 20 miles to the east, 

 which it has left hummocky and worn. Ninety-eight miles west 

 of this the Cabinet Range, 30 to 40 miles long, 7,000 to 10,000 feet 

 high, on the borders of Idaho, shows marked glaciation, the strise 

 having a course 43° south of west. The height, at Libby on Koo- 

 terian, above the sea here is 3,000 feet. The glacial detritus piled 

 along the flanks of this anticlinal is 700 feet in thickness, and 

 represents the material from the gulches. At Hope Pend O'reille 

 Lake the glacial action has undoubtedly been very great, the lake 

 being 3,000 feet deep, with a mountain 4,000 feet above the sea 

 to the north of it. The town is 3,000 above the sea. A number 

 of islands in the lake are scoured down to the water's edge. 

 They represent mountains which may have risen as high as that 



mentioned. The striations are 40° west of north, 43° west of 

 north. A terminal moraine has dammed the river (Clark's Fork 

 of the Columbia), which enters it from the east, and turned it a 

 mile to the south. Pre-glacial action has been active here and at 

 Libby (see above), some 6,000 feet of strata having been removed 

 fromthesummitof the Cabinet anticlinal, most of it beingpre-glacial 

 denudation. Lake Pend O'reille may perhaps fitly be a glacial lake', 

 a rock basin, which has been filled by the waters of the Columbia. 

 The greatest length of the lake is along the strike of the rocks, 

 though this has not been an important feature in moulding its 

 form, but rather the action of glacier, boulders of diabase and 

 granite being observed several hundred feetabovethelakealongthe 

 mountain side. At Clark's Fork, 30 miles east, I observed granite 

 boulders, on a mountain, at a height of 1,800 feet, or about 4,000 

 feet above the sea. Heavy beds of gravels, clays, and boulders 

 fall on the valley of the river (Columbia) for 60 miles, the general 

 direction being east and west. At Thompson the glanier has 

 scoured down a range to the south, the path of the glacier being 

 here apparently south-west. A series of terraces extend along 

 the north side of the river, with large blocks of slates (presumably 

 of pre-Cambrian age) . At Horse Plains a small valley running 

 east and west represents an old post-glacial lake bed. The gla- 

 ciers here came from the north, piling up heaps of clays and 

 gravels along the north hummocky side of the valley. One large 

 erratic block of limestone (upper Cambrian) measured 13 x 15 x 18 

 feet. It was perched about 400 feet above the valley on a diabase 

 dike. This point is 75 miles west of Missoula and about 3,460 

 feet above the sea. At Missoula a large gravel plain (an old lake- 

 bed), of 40 or 50 miles square, lies in the midst of the lower-Cam- 

 brian rocks. To the north the cretaceous rocks dip into the 

 mountains eight miles distant at an angle of 30' north-west. The 

 glaciers have greatly denuded this cretaceous belt into low foot- 

 hills in their path from the mountains (8,000 feet above the sea) 

 8 or 10 miles north. Moraines flank the mountains, large blocks 

 of slates and quartzites from the Cambrian rocks resting at 

 the mouths of creeks and stretching across the old lake beds. 

 Around the mountains a series of beaches or beach-lines extend ; 

 I have counted 36 of them one above the other, extending up- 

 ward for nearly 3,000 feet above the plain. These beach-lines 

 I have traced for 50 miles. They seem to represent a pretty 

 general upheaval following upon the close of the cretaceous 

 period. The depth of the gravels which form the old lake- 

 bottoms must be very great. They consist of Cambrian quartz- 

 ites. To the south of Missoula extends a long valley (terraced) 

 for 75 miles. It lies to the east of a gneissoid range or a bedded 

 quartz porphyry porphroidal or gneiss coeval with Pilot Knob of 

 Missouri and the older Archean gneisses. A glacier undoubtedly 

 travelled to the north, cutting -out a range of Cambrian rocks, 

 dipping south, nine miles south of Missoula, connecting it with 

 the old lake previously mentioned. To the north-west of Missoula 

 are several small valleys, through which the Blackfoot River runs. 

 They all run east and west or nearly so across the strike of the 

 rooks, and are divided by low, rounded, hummocky ranges, over 

 which the glaciers have passed. Stratified gravel deposits are ex- 

 posed along river banks, 75 feet in thickness. One valley, about 

 13 miles long, running along the strike of the rocks, which dip 

 east, has a moraine at its northerly end made of thickly scattered 

 angular boulders and clays, and of a terrace-like nature, rising 200 

 feet above the river, which has here cut through it. Ten miles 

 further north another moraine occurs, and five miles further 

 north a great moiaine of several hundred feet in thickness and 

 holding ponds and small lakes in its surface. These seem to show, 

 so far as a hasty examination would permit, points in the reces- 

 sion of a great glacier whose cour.se was south-west. A few gen- 

 eralizations from these facts show pretty conclusively that, 



1. The rivers are nearly all of pre-glacial origin, but probably 

 post-cretaceous, one or two having been deflected in their courses 

 by the glaciers. 



3. T'ne denudation has been largely, if not in greater part, pre- 

 glacial. 



3. No apparent upheaval has occurred since the glacial period, 

 but a series of beach-lines indicate a pretty general elevation fol- 

 owing the cretaceous period. 



