386 SECTIONAL TRANSACTIONS.—C. 
20. Mr. W. L. T. Apprson.—A Molecular Form of Calcium Carbonate 
accounting for the Crystal Forms of Aragonite and Calcite. 
Any form assumed for a molecule should, to be tenable, account for the 
crystal form or forms in which the compound occurs. 
The concept of the carbon atom arrived at by the stereo-chemist is that of 
a regular tetrahedron. This form also accounts for the crystal forms of carbon. 
‘he carbon or central atom in calcium carbonate would have its space occupa- 
tion extended in one dimension by one oxygen atom and at right angles in a 
second dimension by two oxygen and one calcium atoms. The third dimension 
would arise from the added dimensions of the atom and group of atoms on 
either side of the carbon atom. The space occupation of such a group is roughly 
that of a tetrahedron. é 
The tetrahedron which may be deduced for Aragonite would be an ortho- 
rhombic one of dimensions X 6.7157 : 4.1822: 2.4188 (the molecular volume 
of calcium carbonate being 33.678 in Aragonite). The angle over the short 
edge is 108, 26, 24, a little less than 120 degrees. This angle apparently lends 
itself to the formation of a triad group of molecules which in turn gives rise 
bs 3 OnE atta grouping approximating closely in axes and specific gravity 
alcite. 
Tuesday, August 12. 
Mornina. 
21a. Joint Discussion with Section B (q.v.) on Liquid and 
Powdered Fuels. (Page 377.) 
21b. Discussion on The Pre-Cambrian Rocks of the World. 
(a) Dr. W. G. Mitrer.—The Pre-Cambrian Rocks of Canada. 
As the years go on the pre-Cambrian is of increasing interest, both from the 
scientific and the economic point of view. The relationships of the rocks are 
gradually being unravelled on various continents, and mineral production is 
becoming more widespread. While the oldest pre-Cambrian of most of the con- 
tinents has certain striking characteristics in common, especially the occurrence 
of the peculiar iron formation known as jaspilite, the time has not arrived for 
attempting, with a degree of confidence, the correlation of these most ancient 
rocks of one continent with those of others. All that can be said at present is 
that the resemblance in succession in certain cases is remarkable. 
In the Provinces of Ontario and Quebec, where the pre-Cambrian was first 
studied systematically, and where the rocks were divided into two groups, the 
lower or Laurentian and the upper or Huvronian, later work has shown it to be 
more complex than it was believed to be. It was in 1845, during a trip to Lake 
Timiskaming, that W. E. Logan first saw the conglomerate and other sediments 
to which he afterwards gave the name ‘ Huronian,’ owing to their occurring in 
large volume on the shore of Lake Huron. On this trip to Timiskaming he also 
noted the unconformable relationship of the conglomerate to granite and gneiss 
which came to be known as the Laurentian. More recent work has shown that 
in Northern Ontario there are granites of at least three ages, separated by great 
intervals of time, and the term Laurentian is now applied to the oldest. There 
are also older series of sediments than those that Logan saw lying unconformably 
on the granite of Timiskaming. The following table brings out the relationships 
of the rocks that are now known to occur in the Ccbalt-Lake Timiskaming area. 
Tt also shows that what is now known as the Cobalt series corresponds to Logan’s 
Huronian sediments, and the Algoman to his Laurentian. 
