MINBU. 47 



base of the cone. Now the stream begins to spread out; the 

 walls of the channel gradually diverge (plate VI), driven aside by 

 the pressure of the fresh masses, but still they continue almost to 

 the end of the stream. Inside the walls the mud flows with lesser 

 and lesser speed, partly on account of the small gradient, partly 

 on account of the loss of moisture, and as new masses press on 

 from above, the partly solidified mud cannot move forward, it is 

 therefore raised and shaped into folds which produce a curiously 

 wrinkled surface (plate VI). The wrinkles run transversally 

 across the stream, and more advanced in the centre than at the 

 sides. 



The end of the mud stream, where the loss of moisture is rather 

 rapid, shows a curious rugged structure, resembling very much that 

 of the front of a lava stream. The central part of the mud stream, 

 which looses its moisture less rapidly and dries more slowly, is 

 therefore in a dried state intersected by numerous longitudinal 

 cracks (see plate VI). 



The plates V to VII illustrate these streams ; on plate V is figured 

 the top part of mud volcano No. 5 as it appeared in May 1889; the 

 narrow channel with its raised edges is extremely well seen. Plate 

 VI illustrates the lower end of the same stream as seen from above, 

 the diverging of the side walls, the sigmoidal wrinkles on the centre 

 of the stream, as well as the longitudinal cracks in old dried up 

 streams are well exhibited. Plate VII exhibits the lower part of a 

 mud stream running from the right to the left. 



Origin of the mud volcanoes.— The question why these mud 

 volcanoes should have formed near Minbu only, and not at other loca- 

 lities, such as Yenangyoung or Yenangyat, is a difficult one to answer if 

 we consider that at the two last named localities the same conditions 

 prevail as at Minbu. At Yenangyoung, but particularly at Yenang- 

 yat, there is a high pressure of gas sufficient to produce flowing wells. 

 At both localities the drill has proved that there exist thick 

 layers of clay, and that there is an ample supply of water, in fact 



( 93 ) 



