MINERALOGY. 353 



caisson to the lock, the caisson will rise, and the load of improvement 

 itself recede, and this would be without waste of water, ^o save water 

 To put it in motion with a certain portion of waste, it is 

 presumedjdifFerent ways may be found, as the introduction 

 of a portion of water from the upper canal to the lock, 

 or the discharging of it from the lock to the lower level, 

 these would with management occasion the caisson to rise 

 or fall ; or, if a part of the load were made to shift far- 

 ther from, or nearer to the fixed standards e eee^it would 

 thereby cause the action required, and perform the ope- 

 ration ; and it is^ probable, that a better way than any 

 here suggested would arise, should the thing be put in 

 pr."^ctice. 



I am, Sir, 

 ^ Your obedient humble servant, 



f^ ROBERT SALMON. 



iVoburn, Mat/ 4th, 1805. 

 Charles Taylor, Esq. 



IV. 



Observations^ chieflif mineralogkal, on the Shetland 

 Islands, made in the course of a Tour through those 

 Islands in 1 803. Bi/Dr.T.S. Traill *. 



Ti 



HE first land we made after passing Fair Isle, was the Mineralogy of 

 southern extremity of the Mainland of Shetland. We Shetlaud* 

 approached first to Fitful-Head; a bold promontory 

 composed of micaceous schistus. Pass through Cliff- 

 Sound for several miles. The western side of this narrow 

 channel is formed by a chain of low islands, seemingly 

 composed of micaceous rocks. The eastern side is formed 

 by a ridge of hills, which in many places present craggy 

 precipices of the same material. The rocks along this 

 side are all micaceous. Where Cliff-Sound terminates in 



* Communicated by the Author to Mr. Patrick Neill, A.M. 

 Secretary to the Society of Natural History at Edinburgh, from 

 whose " Tour through some of the Islands of Orkney and Shetland" 

 this article is by permission taken, 



Scalloway 



