50 Tlie A)nen\'(in GeoUxiist. July, 1895 
county, about ten miles froni Rochester, east of soutli. Next 
to the "Turk's hill" mass of drumlinoid drift in the extreme 
southeast corner of the county, the Mendon sand hills are the 
highest land in the county, rising over 840 feet above sea 
level. These hills have an irregular grouping and cover an 
area of nearly four square miles. They can be roughly de- 
scribed as two series of very irregular kames having a general 
direction of S. 30° W., and with a valley between containing 
five ponds. These are the only ponds of note in the county. 
The intermediate valley is lower than the drumlinoid surface 
surrounding the two kame series. The northern pond is the 
largest and highest, having a surface 662 feet above tide. 
The sand hills, therefore, rise above the marsh}'^ valley quite 
two hundred feet. They are exceedingly varied in form, con- 
ical, mammillary, billowy, and enclose basins and kettles. 
The composition is also complex, being mainly fine gravel and 
sand, but with some till. These hills seem to be isolated and 
to have no relation to any moraine or to any line of drainage. 
They are surrounded by heavy drift, distinctly drumlinoid in 
form, the ridges having a direction S. 20°-30° W. 
Summary. 
The " Pinnacle hills" of Rochester, N. Y., are regarded as 
part of a frontal moraine, for the following reasons: 
1. The linear arrangement with distinct curvature. 
2. The continuation of the curve in the well-defined mo- 
raine west of the Genesee river. 
3. The continuation eastward of Irondequoit bay of mo- 
rainic phenomena. 
4. The topography emphatically morainic, "knob and ba- 
sin," with abundant "kettle-holes." 
5. The occurrence of a set of later strije north of the range 
nearly perpendicular or radial to the curving line of the mo- 
raine. 
6. The steep northward slope, with spurs and reentrant 
angles. 
7. The presence of much till in the range, especially upon 
the north side and summits of the belt. 
8. The pushed and tumultuous condition of the beds on the 
north side and crest of the range. 
That the hills were accumulated in the waters of lake 
