364 K O. llovexj—Trap Ridges of the 



railroad, extends in a bold curve to the northward and east- 

 ward for nearly five miles. At the southern end the ridge 

 rises very rapidly to a height of 175 feet, then more gradually 

 until it reaches 240 feet, at a mile aud a quarter from the rail- 

 road. This height is maintained very uniformly for about 

 three miles, though several points are twenty to thirty feet 

 higher and lower, and two points attain 280 feet of elevation — 

 one at the head of the lake and the other a mile farther east. 

 The eastern extremity of the ridge is a bluff rising 160 feet 

 (aneroid measurement), above a small lake at its base, which is 

 perhaps fifty feet above the sea. The slope of the eastern side 

 of the ridge along Saltonstall lake is usually 25° or 30°, while 

 that of the western side varies from 40° and more at the south- 

 ern extremity, and at the bend near the head of the lake to 10° 

 or less, in the curve opposite the middle of the lake ; east of 

 the head of the lake the southern side is usually steeper than 

 the northern. The hluffs, however, are on the convex side. 

 In many places the convex side of the ridge is covered with a 

 heavy talus of trap, while the concave side has comparatively 

 few fragments on it. 



It is hard to determine how much of the ridge is trap and 

 how mnch sandstone. The eastern and southern slopes of the 

 third part of the ridge seem to be composed entirely of trap, 

 except at one point within a mile of the eastern extremity, 

 where sandstone, is exposed high up on the slope. Along the 

 lake most of the rock is solid and hard, but much of it is 

 amygdaloidal in structure, indicating that the present may be 

 nearly the same as the original surface. Shale is exposed on 

 the eastern slope of the second part of the ridge, but neither 

 sandstone nor shale has been observed on the same slope along 

 the first part except at the foot of the lake. The western 

 faces of the first and second parts show well the contact of the 

 trap and underlying sandstone, but the dip of the strata is hard 

 to obtain satisfactorily. On the western and northern slopes 

 of the third part of the ridge no contact has been found. Near 

 the railroad the sandstone rises on the ridge to perhaps eighty 

 feet above sea-level. Measuring in the direction of the dip to 

 the same level on the other side of the ridge, as given on the 

 chart of the Coast Survey (an unsatisfactory method), and tak- 

 ing 40° as the dip of the sandstone at this place, we get 225 

 feet as the thickness of the sheet of trap. Southeast of Lyman 

 Granniss's house (C, on the map), and a mile and a half from 

 the railroad, a trench about 250 feet long was dug into the side 

 of the hill about thirty years ago in a fruitless search for silver. 

 The trench passes through fine, soft shale and ends against 

 fine-grained drab sandstone, which looks as if it had been sub- 

 jected to the action of heat, and is probably very near the 



