A Michigan Preliminary Section. — Grabau. 177 
A PRELIMINARY GEOLOGIC SECTION IN ALPENA 
AND PRESQUE ISLE COUNTIES, MICHIGAN.* 
By Amadeus W. Grabau, Troy, N. Y. 
PLATE XX. 
INTRODUCTION. 
The following section was prepared in the late summer of 
1900, with the assistance of Mr. W. F. Cooper, of the Michi- 
gan geological survey. As no topographical map was availa- 
ble, the profile of the country along the section had to be pre- 
pared in the field, at the time the geological data were collect- 
ed. Distances were measured by means of a cyclometer at- 
tached to the bicycle, which was the only conveyance employed 
in the field. To eliminate errors due to unevenness of the 
country' and to other causes, the cyclometer readings were 
checked by special readings on the section lines. Elevations 
were obtained by reading the aneroid barometer at all the sta- 
tions, as often as these stations were passed, and correcting 
these readings by the barograph record obtained from a sta- 
tionary instrument at Alpena. Owing to the length of the 
section, the barograph corrections did not always prove satis- 
factory, especially as several severe atmospheric disturbances 
affected the aneroid in the northern part of the section, which 
were felt to a less degree at Alpena, where their record was 
obtained by the barograph. 
LOCATION AND EXTENT OF THE SECTION. 
The section is located in Alpena and Presque Isle counties, 
Michigan. It runs north from the city of Alpena along the 
meridian of 83° 27' longitude west of Greenwich, and forms 
the western boundary of the eastern third of range 8 E. It ex- 
tends through the whole of townships 32 and 33 north and 
parts of townships 31 and 34 north. The total length of the 
section is nearly eighteen miles, but the distance covered in its 
preparation was nearly double that. 
The section is interrupted near the middle by Long lake, 
and it passes by the eastern end of Grand lake. It strikes tlie 
shore of lake Huron about four miles southeast of Presque Isle 
♦Published by permission of Dr. A. C. Lane, State Geologist. 
