6o OSCAR H. HER SHE Y 



preceding with the addition generally of Canadian pebbles and 

 small bowlders. Usually seen in marginal deposits. 



Class IV. Typical till. Light yellow gray calcareous clay 

 containing pebbles and small bowlders of local and foreign 

 derivation, many of the latter beautifully striated. 



The divisional lines between these classes, in the Pecatonica 

 basin, must always be arbitrarily placed, as there are gradations 

 from those deposits which are typical of one class to those which 

 are typical of another. There is, also, no definite rule in their 

 distribution for, while the four classes evidently represent four 

 successive general stages in the process of manufacturing typical 

 till, and should, therefore, naturally be expected to occupy suc- 

 cessive belts from the outer glacial boundary back or east, they 

 are in reality scattered indiscriminately over the entire district. 

 However, Class I prevails in the northern half of the county ; 

 Class 11 in a north and south belt which, extending across the 

 county, has its western boundary on a meridianal line which 

 passes a few miles west of Freeport, and dies away to the east 

 near the Winnebago county line ; Class III prevails over a belt 

 several miles in width extending diagonally from the south- 

 eastern corner of the county to near Freeport ; and Class IV is 

 principally developed south of Yellow creek, over and near to 

 the remnants of the Lake Pecatonica clays. 



Perhaps the most remarkable feature of the drift of this 

 county is its anomalous distribution. Over the western one- 

 third of the county, the drift, although comparatively thin, is 

 generally distributed. Over the central belt, the evidence of 

 vigorous glacial action is strongest. While in the extreme 

 eastern one-fourth of the county, which was glaciated longest, 

 there is very little drift of any kind, and there are areas, several 

 square miles in extent, of nearly bare rock, and others where 

 the preglacial residuary clay still remains undisturbed. It is 

 evident that the conditions which controlled glacial action 

 varied locally within wide limits, so that excessive abrasion [of 

 the rock surface might occur with a less weight of ice and a less 

 length of glaciation, than on a neighboring area with similar 



