STRLE OF THE SCIOTO LOBE. 425 



The general absence of striiB on the numerous outcrops of Umestone in 

 the highlands of Logan and Champaign counties has been a cause of sur- 

 prise, for they abound on either side and north of these highlands at nearly 

 every outcrop examined. An exceptionally careful search was made for 

 them in the highlands, as it was deemed important to gather all possible 

 evidence shedding light upon the direction of ice movement at the junction 

 of the Miami and Scioto lobes. Their absence seems to indicate that the 

 abrasion was less vigorous in the morainic area than it was a few miles back 

 beneath the ice, though the amount of drift deposited there was not less, 

 but instead rather more, than in the region within the morainic system. 



South from Champaign County there is scarcely a rock outcrop along 

 the moraine or the inner border plain for a distance of 40 miles or more, 

 which accounts for the lack of observations of strife in that region. South- 

 west from this moraine, where the drift is thinner, striae are found in nearly 

 every exposure examined between it and the outer moraine, and in the dis- 

 trict farther west covered by the Miami lobe. The ice movement appears, 

 therefore, to have been vigorous in the terminal portions of the lobe. 



The small number of striae observed near the eastern border of the 

 Scioto lobe and southern border of the shelf or shoulder is probably due in 

 large part to the texture of the rock. The shales in the southeast part of 

 the lobe coidd scarcely retain striae long after exposure, as they soon 

 crumble and decay. The coarse sandstone farther north is often of a loose 

 texture, so that striae could not be preserved. The outcrops of Waverly 

 sandstone are not extensive in the region investigated, and only certain 

 layers of the formation would retain striae after long exposure. 



The large number of striated exposures reported from the vicinity of 

 the Cuyahoga River is due to their remarkably peifect preservation on the 

 Eocarboniferous conglomerate, and that, too, in the most exposed situations, 

 where there has been little or no drift covering the rock since the ice dis- 

 appeared. The sandstones in that region, being a firm grit rock, are also 

 more suitable for retaining striae than in the regions farther west and south, 

 where they are soft. The causes for the variation in frequency of observa- 

 tions of striae in different parts of the lobe embrace, therefore, differences 

 (1) in abrading power of the ice sheet, (2) in concealment by drift, and 

 (3) in the texture of the surface rocks. 



