and the Northern part of New York Island. 427 
tion of the stem, the amount and direction of the pitch or dip 
of the beds. For the convenience of the reader, I repeat the 
Tatios between the stem of the T and half its top which are adopted 
to express the angles of dip. 
Dip of 80° a ratio of 1 : 4 Dip of 35° a ratio of 5: 4 
70° 14:4 25° 6:4 
x : 20° 7:4 
50° oS 4 15° 8:4 
45° 10° 9:4 
4:4 
Dip of 5° a ratio of 10: 4 
Consequence of local flexures or undulations in the stratifica- 
tion; as in fig. 24 (the dips indicated by which are 25° and 
45°), And when such local flexures arch over, the symbol 
approximately horizontal), as in fig. 25. 
* On a large ipt map, a convenient length for the top of the T is eight 
millimeters ; and this adopted, the above ratios are in mi imeters. Or, if the top is 
made one-third of an inch long (about eight and one-half millimeters), the ratios 
are in twenty-fourths of an inch. 
