GLACIAL DRIFT UNDER SAINT LOUIS LOESS 497 



Several pebbles of characteristic sub angular shape and of a compo- 

 sition which shows them to be erratics are shown in Figs. 2 and 3. 

 Fig. 3, ^, is a ferruginous chert. It bears a resemblance to pebbles 

 in a conglomerate at the base of the Sioux quartzite of southern Min- 

 nesota and northern Iowa. Cherts of this sort are also found, however, 

 in the Mesabi and Penokee iron ranges of northern Michigan. Fig. 

 3, 5, is a planed and polished pebble of dark-blue felsite which con- 

 tains phenocrysts of feldspar and quartz. Fig. 3, C, is a sandstone 

 with hematite cement, approaching a quartzite. In Fig. 2, A and B 

 are quartzite resembling that at Sioux Falls, la. ; C and D are medium- 

 grained greenstone, planed on three faces. Pebbles and bowlders 

 representing the following rocks are found in this section : coarse sand- 

 stone, almost a quartzite, with silica and hmonite cement; sandstone 

 with hematite cement; quartzite; vein quartz; quartz porphyry; 

 felsite; greenstone; biotite granite; pegmatite. While all these 

 varieties might have come either from the southern Minnesota district 

 or the Lake Superior district, it seems rather probable that the drift 

 came from the former direction. This district is nearer than that 

 of northern Michigan; and a southward direction of transportation 

 would agree with Leverett's observations of pebbles from Calhoun 

 and Lincoln counties. 



From Meramec St. southward for several blocks exposures of 

 bowlder clay of varying thickness may be seen. Near the Hoffman- 

 Hogan quarry is an outcrop resembling the one at Grand Ave. and 

 Rutger St., described in this paper. Rhyolite, granite, and diabase 

 pebbles have been found by the writer in these exposures. 



While it is possible that in certain places the thin sheet of gravelly 

 material under the St. Louis loess is glacial gravel, as described by 

 some authors, rather than till, the sections described in this paper 

 are without doubt true bowlder clay. The variety in composition of 

 the pebbles and bowlders indicates collection from distant and scattered 

 sources, and transportation by an ice sheet. The presence of many 

 subangular pebbles with smooth and planed sides, associated with 

 pebbles of less characteristic shapes, the heterogeneous mixture of 

 bowlders, pebbles, and fine clay, and the compactness and general 

 consistency of this clay, are all indicative of till rather than of a water- 

 made deposit. This sheet of drift has been observed by the writer 



