DEPOSITS ON BOULDER RIDGE 699 



gravels" represent the insoluble weathered residuals at the top of the 

 older drift. Taking everything into consideration, it is clear that the 

 heavy drift forming the capping of Saint Mary Eidge can not be re- 

 ferred to the last Saint Mary glacier, although that ice-stream so far 

 filled the valley as to overtop the high slope of the ridge east of the 

 lower lake. 



Deposits on Ridge west of Lower Saint Mary Lake 



On the west side of Lower Saint Mary Lake a correlative, but some- 

 what smaller ridge of Cretaceous shale and sandstone lies between the 

 lake on the east and Flattop Mountain and Boulder Creek Valley on the 

 west. The crest of the ridge is narrow and serrate, consisting of a row 

 of sharp hills extending north-south on the line between sections 16 and 

 17, township 35 north, range 14 west. These peaks stand 5,700 to 5,900 

 feet above sealevel, 1,200 to 1,400 feet above the lake, and 500 to 700 

 feet above Boulder Creek. There is no very good exposure, but the ma- 

 terial seen on the surfaces of the knobs is like that of the drift described 

 above. Mr. Campbell reported that he found tillite conglomerate on top 

 of one of the hills. It is probable that this is a remnant of the pre- 

 Wisconsin drift. The surface of the ridge surrounding the line of hills 

 is marked by low swells and sags, the result of later drift deposition or 

 of landsliding or a combination of both. 



Deposits on Boulder Ridge 



On the crest of the Cretaceous ridge between Boulder and Swiftcur- 

 rent creeks is a heavy deposit of glacial till which appears to be 200 feet 

 or more in thickness. This is exposed in fresh scarps due to slumping 

 at two or three places at the tops of the north and south slopes. The 

 pebbles and boulders in the reddish till are of limestone, red and green 

 argillite, quartzite and diorite, and are well facetted and striated. Ledges 

 of tillite conglomerate due to cementation protrude from the drift slope, 

 but there is no notable evidence of weathering and limestone pebbles arq 

 present nearly or quite to the top. The top of this highest part of 

 Boulder Ridge is notably flat, like the crest of Two Medicine Ridge, and 

 has a length of about 2 miles. In this length the elevation increases 

 southwestward toward the mountain from about 6,100 to 6,300 feet 

 above tidewater. It thus stands 600 to 800 feet above Boulder Creek on 

 the south and 1,400 to 1,600 feet above Sherburne Lakes in Swiftcurrent 

 Valley on the north. At the southwest end of this flat top a short sharp 

 ridge rises to an elevation of 6,400 feet above the sea. The rise does not 

 XLIX— Bull. Geol. Soc. Am., Vol. 23, 1911 



