A CONTRIBUTION TO THE STUDY OF ICE-STRUCTURES 13 



strongly prismatic. In that position patches of tube-like bubbles appeared, usually 

 straight but often winding, averaging a thirty-second of an inch in diameter. At thirty 

 inches below the surface of the stratified lake-ice prisms were met with as much as 

 three inches in cross-section and nine inches long. At that horizon the average cross- 

 diameter was one inch. Occasional bubbles in this part were pear-shaped with the larger 

 end uppermost. 



At, and below this level, the ice was very clear and exhibited a well-developed con- 

 choidal fracture with distinct flutings across the sweeping curves. These latter radial 

 flutings became increasingly more strongly marked in the deeper levels. Descending 

 still further, the prisms began to contract in size so that at a depth of eight feet below 

 the surface of the coralloidal ice the grain size was found to average a third of an inch. 

 At that place scattered irregular bubbles were met with, all exhibiting a tendency to 

 elongation in the vertical direction. A block measuring 450 cubic centimetres was 

 found to contain twenty-three bubbles, or one per twenty cubic centimetres. 



(7 ) Between the depths of nine feet and eleven feet below the surface of the coralloidal 

 layer was a band of coarse vertical prismatic ice containing fragments of the red-brown 

 alga on which Murray found living microscopic life. The fragments of alga were each 

 enclosed within disc-like gaseous envelopes, the gas apparently breathed out by the 

 plant and microscopic animals at the time of freezing. As an instance may be mentioned 

 a fragment of alga, half an inch in diameter, surrounded by a gaseous disc five inches in 

 diameter and one-eighth of an inch thick. Adjacent to one of the alga fragments was 

 a bunch of vertical gas-tubes (see Plate II, Fig. 3). At the ten-foot level a zone of 

 beautiful tubes was cut through ; these had a bulbous extremity below and extended 

 upwards in a regular stem as much as six inches ; their diameters ranged from a sixteenth 

 to a twelfth of an inch. A slab of ice from about this level showed tubes from two 

 inches to three inches long and one-eighth of an inch in diameter. On close inspection 

 these were found to be beautiful negative hexagonal crystals. As many as 150 were 

 counted in the slab which, in cross-section, measured 525 square centimetres. Where 

 more sparse they were larger. Examined with a pocket lens they were found to be drusy 

 in the interior. 



(8) Below eleven feet there was a change in the ice, so concluding the evidence which 

 indicated that at one time that was the downward limit of thaw for one or more seasons. 



From eleven feet onwards bubbles were but occasional. Here and there large 

 irregular ones showed along old fracture planes which had become recemented. The 

 ice was still prism-ice, but no individual longer than three inches was noted. The radial 

 flutings crossing the conchoidal fracture curves were strongly marked. 



At fourteen feet to fifteen feet the jarring of the pick developed sets of wavy horizontal 

 cracks, the planes of which crossed each other and resulted in an appearance reminding one 

 of augen structure. Evidently the effect of strain induced by the superincumbent weight. 



At fifteen feet the rock bottom was reached. There remains of the alga were 

 found. In association with it abundant unicellular chlorophyll-bearing organisms, 

 rotifers, etc., were found still living. The evidence already mentioned goes to show 

 that these organisms must have been imprisoned there in the frozen state for at least 

 three years and probably a great deal longer. 



In explanation of the persistence of live organisms in the depths of some of the lakes 

 at Cape Royds, which have remained frozen over in all probability for years, it is 

 suggested that, as sunlight can penetrate through the ice, so long as there is a balance 

 between the plant and animal life all will thrive just as well under a roof of ice as 

 free from it. On account of the lower freezing temperature of saline water, the briny 

 portions of the lakes are the last to solidify and, except in the deepest lakes, are doubtless 

 also the first to thaw. As this is so, the organisms should be able to live on for the 



