MED WAY SPETNGS. 319 



feet, when the legs were bent at right angles to the body. This rim is 

 only about six inches in thickness. An analysis of the tufa of which it is 

 formed was made by Mr. E. W.* Woodward, with the following result : 



Lime 53.22 



Ferric oxide 0.22 



Carbonic acid 41.73 



Sulphuric acid 2.38 



Insoluble residue 2.49 



100.04 



No analysis was made of the waters, but, from the composition of the 

 tufa, it is seen that the main constituents must be carbonate, with a little 

 sulphate of lime. From some of the springs is a slight escape of carbonic- 

 acid gas; others, again, have a slight odor of sulphuretted hydrogen, which 

 may probably arise from the decomposition of the sulphate in contact with 

 organic matter. The amount of iron evidently varies considerably, as 

 around some springs the surface is stained for a considerable distance with 

 a deposit of hydrated oxide of iron, while at the above spring none was 

 observable to the eye. In temperature, the springs are generally from 70° 

 to 110°, but in some instances reach nearly the boiling point. The tem- 

 perature evidently depends more upon the amount of surface exposed to 

 the air than upon a variation of the original temperature of the water as it 

 comes from below. 



On the foot-hills to the north of the town of Medway was found a bed- 

 ded deposit of volcanic ash adjoining the trachyte body, which would seem 

 to indicate that the valley was filled with water at the time of the trachyte 

 outflow. In the valley-bottom, above the bend of the Provo, toward Silver 

 Creek, is found a light-gray porous trachyte, which also has the appearance 

 of having been ejected under water ; it is composed of a white pumice- 

 like groundmass, in which are large crystals of sanidin and needle-like prisms 

 of black hornblende, together with mica. The divide between the Provo 

 and the headwaters of Silver Creek is formed of a remarkably beautiful 

 variety of trachj^te, generally of reddish-purple color. It is made up very 

 largely of well-defined crystals of sanidin, with black and somewhat 



