SUB-LACDSTRAL SPRING DEPOSITS. 



61 



comes in contact witli the colder and more dense waters of the lake A 

 few of the deposits from these springs are represented, half natural size in 



the followinji- figrure: 



Pig. 6. — Deposits of calcium cai bonate from sub-laciistral springs. 



Among The Needles the rocky capes are connected by crescent-shaped 

 beaches of clean, creamy sands, over which the summer surf breaks with 

 soft murmurs. These sands are oolitic in structure, and are formed of con- 

 centric layers of carbonate of lime which is being deposited near where 

 the warm springs rise in the shallow margin of the lake. In places these 

 grains have increased by continual accretion until they are a qviarter 

 of an inch or more in diameter, and form gravel, or pisolite, as it 

 would be termed by mineralogists. In a few localities this material has 

 been cemented into a solid rock, and forms an oolitic limestone suffieieutlv 

 compact to receive a polish. Xo more attractive place can be found for the 

 bather than these secluded coves, with their beaches of pearl-like pebbles, or 

 the rocky capes, washed by pellucid waters, that ofFer tem])ting leaps to the 

 bold diver. The tufa forming The Needles is grav in ton(>, with a light- 

 colored band, 10 or 12 feet broad at the base, consisting of a coating of 

 very recent calcareous deposit, similar to that forming the oolitic sands, 

 but probabl}' not dependent on spring action. On the clifts the nucleus 

 about which the lime crystallized was innnovable, and became coated with 

 a continuous layer of calcium carbonate; on the beach the sands were 

 washed about by the waves, and grew into little spheres of polished marble. 

 A band of recently-formed tufa, like that surrounding tlie base of The 



