[whittaker] bottom DEPOSITS OF McKAY LAKE 151 



material became dry the laminae tended to pull apart and render 

 themselves more apparent. 



The olive green ooze of bed c was of much softer composition 

 than either those above or below. The laminae are hard to differen- 

 tiate though a double layer of calcium carbonate about 15^ inches 

 above the base of the sections is readily distinguished by contrast 

 with the rest of the section. This is shown in the photo of the section, 

 Plate II, Fig. B, at point marked M. 



The chocolate brown ooze with its alternating grey and chocolate 

 laminae is most interesting of all. In this band alone was it possible 

 to actually count the laminae with a fair degree of accuracy and by 

 actual count there are about 440 double laminae (one grey and one 

 chocolate lamina). In Plate II, Fig. A, representing this material, 

 the pins are separated from each other by 100 double laminae." Meas- 

 urements of the thickness of these laminae over the whole thickness 

 of these bands gave an average thickness for a double lamina of .017". 

 Hence each grey or chocolate band would average only .008" or less 

 than one one-hundredth of an inch . This thickness is, of course, in the 

 compressed sediments. Above these laminae are some beds of ooze 

 which are not differentiated into laminae. The uppermost ooze, zone 

 a, consists of very soft material. In some of the samples it is quite 

 black and tenuous with a thin layer of calcareous material in it. This 

 layer owing to its lack of body is very difficult to secure and though in 

 some samples it seems almost absent and in others as much as two 

 inches thicks it is probably a fairly uniform band which is lost in some 

 cases while being removed from the water. 



In the section photographed all the laminae instead of being 

 perfectly level were pulled down on one side. This was due to one 

 side of the cutting edge of the sampler being rougher than the other 

 and this consequently bruised and compressed the ooze causing that 

 side to drag as it was pushed up the sampler tube. It is the same 

 friction between the side of the tube and oozes that causes them to 

 be compressed to such a great extent. 



It is thus seen that the above core from the bottom of McKay 

 Lake, excluding certain marly layers, is largely an ecological succession. 

 When algae and diatoms only are contributing to deposition in the 

 centre of the lake the yearly deposit is rather small. For even if lime 

 were deposited it would redissolve owing to the large quantity of 

 carbon dioxide present. The fact that in this lake the epidermis of 

 the valves of the thick shelled unionidae, from which the calcium 

 carbonate has been completely removed, remains, shows this to be 

 a probability. 



