4 GEOLOGY. 



pous structure, falling into angular pieces. To this rock we 

 are indebted for nearly all our cascades- It often forms preci- 

 pices, over which the mountain streams leap, and foam with 

 great beauty. Katay river descends several hundred feet over 

 a succession of these precipices ; and on the east side of the 

 mountains, nearly in the latitude of Tavoy, is the finest fall 

 I have seen in the provinces. At this place Hidu river falls 

 into a chasm some seventy feet deep, with banks for several 

 hundred yards, as high and precipitous as the wall over which 

 the stream plunges. 



IGNEOUS DYKES. 



Igneous dykes are not uncommon, but they bear very lit- 

 tle resemblance in their mineral contents to the ordinary trap 

 rocks of Europe and America. Some resemble quartz rock, 

 others appear like altered rocks, and many look like sand- 

 stone, which has been subjected to the action of fire. That 

 they have been ejected in a soft state is clear from their sides, 

 which in some places abound with hemispherical cavities, into 

 which the soft shales have been pressed, and their pressure 

 probably produced the cavities. The shales are sometimes 

 seen pressed upwards many degrees on the upper side of the 

 dyke. 



A remarkable dyke is seen in the upper part of the Tenas- 

 serim river. It runs like a wall nearly half way across the 

 stream, and is called by the natives the "Giant's dam." It is 

 about twenty feet high above the water, five or six feet thick, 

 with perfect parallel sides, and is inclined some ten or fifteen 

 degrees from a perpendicular. It is a silicious rock, with no 

 traces of hornblende in its composition. 



Some of these igneous rocks appear in hand-specimens to 

 resemble grauwacke ; and they have been confidently pro- 

 nounced to be grauwacke, but when viewed in connection 

 with other rocks in situ, their igneous origin is quite appa- 

 rent. 



claystone porphyry. 



Among the sla es and sandstones of Tavoy, claystone por- 

 phyry is often seen, but I have never met with it at Maulmain, 

 nor any where in Province Amherst. Excepting the mural 

 masses of limestone, that province is an immense flat east- 



