22 Report on the Magnetic Survey. [No. 1. 



58 of a coloured scale in the plains, and number 30 on Phulloot, 

 decreasing consequently with elevation. 



From Phulloot, a particular modification in the transparency of 

 the air was observed June 4th. A few minutes after sunrise the 

 shadow of the mountain was seen as plainly as possible, and never- 

 theless all the objects in the same direction were visible, only a little 

 less distinct, through it, the fine haze being just thick enough to 

 show the limits between its illuminated and shaded part, and allow- 

 ing objects at the same time to be seen through it, as through a 

 very thin curtain. 



IV. — Geological Observations. 



In Sikkim the rocks are all crystalline and metamorphic without 

 limits so well defined as to enable me to distinguish them in a geolo- 

 gical map ; but in these districts, the direction of joints and cleavage 

 showed many interesting relations with the form and direction of the 

 valleys and with the inclination of the surface. 



The cleavage has a predominant dip to N. 45° E. and is gener- 

 ally very steep, which causes not unfrequently the slopes of the 

 mountains to be steeper, where they coincide with the direction of 

 the surface of the stratification, than on the opposite flanks. 



In the valley of the Mahanuddy, two miles below its junction with 

 the Eatiang, a system of sandstone containing tertiary coal was 

 examined. 



The coal at this place is of very good quality, but does not reach 

 the surface in very large masses ; more of the same coal is to be seen 

 on the left shore of the Mahanuddy. 



The sandstones dipped to N. 6° E. inclination 30° ; they are fol- 

 lowed by marls, probably corresponding in age to the limestone 

 overlying the coal in the Khosia hills. 



In the Khosia hills, the valuable geological map of Mr. Oldham 

 allowed of but few additions, and these particularly in reference to 

 cleavages. I found one direction of the cleavage in the sandstones on 

 the surface of the plateau of Cherra, coinciding with one system of 

 cleavage in the gneiss at the foot of the hills ; several other systems of 

 cleavage are decidedly different in the different succession of rocks.* 



* The collection of stones now sent to Calcutta contains 500 to 600 specimens. 



