in THE HOT SPRINGS 23 



a mile above Ndavutu. If the above statement of the natives is 

 correct, as I believe it is, then these thermal springs issue along a 

 line quite four geographical miles in length extending inland from 

 the mouth of the Wainunu. 



All the springs are situated in the tidal part of the river-valley, 

 with the exception of that of Thongea, which is just above this 

 limit. They are but little elevated above the sea-level, those ex- 

 posed being usually not more than ten feet above the river and 

 often much less. This is a region of basalt, the valley of the 

 Wainunu lying, as described on page 82, in the fold between two 

 great basaltic flows, and probably representing a line of weakness, 

 along which the hot springs issue either from among loose blocks, 

 or from the soil, or from a tufaceous sandstone. They deposit 

 little if any of the siliceous sinter which is often found in the ther- 

 mal waters of this island. This is due probably to their scanty 

 exposure and to their low temperature. The density of the water 

 is near that of fresh water, being not over 1001. The following 

 temperatures may be useful for comparison with future observations : 



Thongea, when not covered by the stream July, 1898, I27°F^ 



Ndavutu, bath-spring at Mr. Barratt's house Usually ioo° „ 



„ on left bank of the creek near the landing place . June, 1898, 126 „, 

 „ on left bank of creek near mouth Dec. „ 127 „, 



„ pool in foot-path on left bank I June 2, „ 112 „, 



" * ! July 27, „ iii° „ 



,, at bottom of main river in depth of 3 feet, close^ 



to the left bank and just above the mouth \ T , 



of the Ndavutu creek, self-registering Six f 



thermometer used ' 



2. The Hot Springs of Natoarau and its Vicinity. — This 

 thermal system lies in the lower valley of the Mbale-mbale branch 

 of the river Ndreke-ni-wai. The principal springs are situated at 

 Natoarau, a village about half a mile in a direct line from Mbale- 

 mbale, about three miles from the coast, and only about fifty feet 

 above the sea. They bubble up in pools near brooks, and extend 

 at intervals over an area probably several hundred yards across. 

 Five springs came under my notice ; but there are doubtless several 

 others in the low-lying and often swampy land of this district. No 

 deposits were noticed, but the mode of occurrence and low temper- 

 ature of the springs serve to explain this fact. The following 

 temperature observations were made by me in March, 1899 : — 



A. Pool 4 feet across, with sides of stone, close to village . . 126 F. 



B. Pool 10 feet wide, a few paces from pool A 114 „ 



