222 STBEAM TIN DEPOSITS OP PERAK. 



and its fractured edges show that it has been detached from a more 

 massive rock by the exercise of some force. But I shall reserve 

 for another occasion what I have to say about this piece of stone. 



The second stone is water-worn. Whatever shape it had for- 

 merly, that shape has been modified by the action of a running stream. 

 No other natural action gives to stones the peculiar smooth and 

 rounded shape that this stone has. It has not, however, been pro- 

 duced by water alone. There has been also the grinding action of 

 friction by one stone upon another. Running streams have their 

 gravel in constant motion. By carrying away sand and lighter par- 

 tides, the large stones are constantly shifting their position and roll- 

 ing over. Then a flood comes, and the stones are pushed along and 

 pounded against one another until the edges of the fragments have 

 abraded and rounded. This process of hammering, breaking and 

 washing is one that is constantly going on. It is more rapid of 

 course and constant in swift deep streams. Irregular as it would 

 seem, modern science has found means to measure it. By the use 

 of the water telescope and by actual experiment, Mons. Daubbee 

 has learned much that formerly was, in this matter, mere conjecture. 

 By means of revolving cylinders, be found that when pieces of gra- 

 nite are subjected to the kind of movement and friction met with 

 in rivers, they are reduced to fine mud when they have traversed a 

 distance of about 25 miles. 



One word here about this granitic mud, which will form subse- 

 quently a subject of our enquiry. Though the change from a rough 

 piece of granite to mere fine mud is very great, yet it is not so com- 

 plete as to elude detection by the microscope. With the aid of this 

 instrument, an expert can tell you at once that such mud has been 

 derived from granite. He can not only tell you what kind of gra- 

 nite it was, but also whether it contained any. metals. He can also 

 say with certainty whether it was the action of the sea or rivers 

 which reduced it to mud, and many other particulars which we shall 

 find hereafter most useful in our present enquiries. 



It may seem very unnecessary to spend so much time in ex- 

 plaining so simple a thing as the manner in which stones become 

 water-worn. But obvious as it is, I think you will acknowledge its 

 importance if you will bear with me a little longer. Simple also 

 as it is, several important geological conclusions depend upon it ; 

 and in fact, like most simple things in nature, when closely ob- 

 served, it serves to explain what is very complex. Thus, if you pay 

 attention to the hills and mountains which surround the beautiful 

 valleys near Thaipeng, you will notice features which this water- 

 worn piece of stone will help you to explain. Our mountain 



