476 EEPOBT — 1891. 



Curve II.— Spring Mill Reservoir, Eochdale. 9 A.M. 

 Air y^'aier 



Oldham Resekvoirs. 



The weekly means of Pietliorn and Densliaw reservoirs are given in 

 Curves Nos. III. and IV. Both reservoirs are situated in a region the pre- 

 vailing formation of which is Millstone grit. Piethorn reservoir Las an 

 area of 40 acres, a depth of 58 feet, and a capacity of 344 million gallons. 

 Its surface is 823 feet above sea level. Denshaw reservoir is of smaller 

 size, 23 acres, with a depth of 54 feet, and capacity of 146 million 

 gallons, and it stands 1,000 feet above the sea. Piethorn may be com- 

 pared in elevation with Cowm and Spring Mill reservoirs, referred to 

 above, and it is interesting to compare the respective temperatures. 



Discussion of Temperature Ohservations on Air and Water at Pietliorn and 

 Benshaiv. By Mr. William Watts, F.G.S. 



The temperature observations of the atmospheric air and water taken 

 at Piethorn and Denshaw have been in accordance with the instructions 

 of the Committee, and under the auspices of the Manchester Geological 

 Society. The area and capacity of each reservoir remain unchanged, 

 and the readings are taken daily at 9 a.m. A higher temperature both 

 of atmospheric air and water is still maintained at Piethorn, although 

 the two valleys are near together, similar in their geological substrata, 

 and not much unlike in their physical conformation. Trees in both 

 valleys are scarce and grow with difficulty, although in former times 

 they appear to have flourished luxuriantly at a much higher elevation 

 than we find them existing now. The absence of trees is to be explained 

 rather by the keen north-east winds to which the valleys are exposed, 

 and by the rapid denudation of the valley sides by rain which washes 

 the soil from the roots, than by the pollution of the atmosphere by 

 factory smoke. A glance at the tables shovrs that the water is warmer 



