514 Notices of Memoirs — Glaciation of North- Central Canada. 



was so arranged that the pressure might be maintained for weeks, 

 or even months, if required. Under these cii'cumstances, the con- 

 ditions of pressui'e to which the marble is subjected are those in the 

 " zone of flow " of the earth's crust — those, namely, of a pressure 

 above that of its elastic limit, while yet unable to break in the 

 ordinary manner, owing to the tube which confines it having a still 

 higher elastic limit. Under the pressure, which was applied 

 gradually and in some cases continued for several weeks, the tube 

 was found to slowly bulge until a very marked enlargement of the 

 portion surrounding the marble had taken place. The tube was 

 then cut through longitudinally by means of a milling machine 

 along two lines opposite one another. 



The marble within, however, was still firm, and held the respective 

 sides of the iron tube, now completely separated, so tightly together 

 that it was impossible without mechanical aids to tear these apart. 

 By means of a wedge, however, they could be separated, splitting 

 the marble through longitudinally. The column in one experiment 

 was reduced from 40 millimetres to 21 millimetres in height. The 

 deformed marble differs from the original rock in having a dead 

 white colour, the glistening cleavage faces of calcite being no longer 

 visible, and although not so hard as the original rock, it is still firm 

 and compact, and especially so when its deformation has been carried 

 out very slowly. No accurate measurements as to its strength have 

 yet been made, but it will withstand a sharp blow, and fragments of 

 it, weighing 10 grams, have been allowed to fall through a height of 

 over 2^ metres (8 feet) on to a wooden platform, from which it 

 rebounded without breaking. Thin sections of the deformed marble, 

 when examined under the microscope, show that the calcite in- 

 dividuals composing the rock have in many cases been twisted and 

 flattened, and in the majority of cases a very fine polysynthetic 

 pressure-twinning has been induced in them, with movement along 

 gliding planes, as well as several other structures seen in nature in 

 highly deformed rocks. 



The experiments therefore show that limestone, even when dry 

 and at ordinary temperatures, does possess a certain degree of 

 plasticity, and can be made to " flow," the movements set up 

 developing many structures which are characteristic of rocks which 

 have been squeezed or folded in the deeper portions of our earth's crust. 



II. — The Glaciation of North-Central Canada. By J. B. Tyrrell. 



IN the region immediately west of Hudson Baj' the earliest glacia- 

 tion of which any traces were recognized, flowed outwards from 

 a gathering-ground which lay north or north-west of Doobaunt Lake. 

 Subsequently this gathering-ground moved south-eastward, until it 

 centred over the country between Doobaunt and Yath-kyed Lakes. 

 From one or other of these centres the ice seems, to the writer, to 

 have flowed westward and south-westward to within a short distance 

 of the base of the Eocky Mountains ; southward, for more than 1,600 

 miles to the States of Iowa and Illinois ; eastward into the basin of 

 Hudson Bay ; and northward into the Arctic Ocean. 



