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pure white, and very slightly coherent. A block placed in 
water breaks down like loaf sugar. In procuring fossils a large 
block was placed in a pail of water and allowed to soak for 
some hours. As most of the shells contained small quantities 
of air, they floated to the top when the block disintegrated, 
and were removed with a sieve. A partial account of the 
McKay Lake fauna has already been published . 1 , 
At Colton lake and at Mink lake the marls occur only a 
short distance above the present water level, and on account of 
the greater differentiation of the fauna, as well as the slightly 
fresher appearance of some of the shells, it would appear that 
the McKay Lake deposit is much older than the others. 
GENERAL CHARACTERISTICS OF THE FAUNA 
Most of the specimens are so perfectly preserved that the 
finest ornamentation remains unabraded, but the original colour 
has been lost and most of the shells are pure white. In addition 
to the freshwater species, a few terrestrial molluscs which are 
found in the marl beds are included in the description of the 
fauna. Such forms, of course, have been washed accidentally 
into the water. In the descriptions of the species which follow, 
the characteristics of the living animal and the colour of the 
shell when living have been omitted, so that only those char- 
acters which can be recognized in fossil forms have been enu- 
merated. Certain genera and species are difficult to differentiate 
in the fossil state, as they have been founded on anatomical 
differences in the living animal. As most of these species are 
still extant, this description may be used to identify these forms 
in present lakes and streams, so far as this may be done from 
shell characters. 
1 Whittaker, E. J., “The relationships of the fossil marl fauna of McKay 
lake, Ottawa, to the present molluscan fauna of the lake." Ottawa Naturalist, 
vol. 32, No. 1, April, 1918. 
