TRANSACTIONS OF SECTION C. 6G5 



imaginary as may be thought at first sight. Such forces, exerted under lilie 

 conditions upon the mass of the earth, ever struggling, as it were, for 

 supremacy, and meeting with all the varying resistances due to widely differing 

 qualities of material, are necessarily sources of an enormous generation of heat 

 wherever a readjustment of that material, even to the slightest extent, ensues. 

 If we conceive such a movement of compressed matter upon itself at a depth of, 

 say, two or three miles within the substance of the earth, a development of heat 

 must occur which, on the release of the strain, will result in the fusion of those 

 particles around large areas of disturbance. 



Amongst the many indications of such actions, instances can be quoted where 

 the maxima and minima of chronic volcanic eruption are demonstrably concurrent 

 with those of the tidal strain. In the same manner we can trace to this constant 

 variation of strains many of the more permanent evidences in geological structure, 

 such as the formation of fissure veins and the lamination of igneous rocks — a 

 process wholly distinct from that of sedimentary strata deposited by the action of 

 fluctuating currents of water. The columnar structure of basaltic rocks caused 

 by a gradual release from compressive strain acting equally in all directions may 

 also be illustrated by a small scale experiment. 



5. Palceozoic Geografhy of the Eastern States. 

 By E. W. Claypole, B.A., D.Sc, London. 



An attempt to sketch in outline the general course of the geographical and 

 hydrographical changes which marked the mid-Palaeozoic eras in the eastern part 

 of the United States. The subdivision of the Silurian and Devonian eras is carried 

 as far as attainable data allow, and the extinct geography shown by a series of 

 lantern-slides. 



6. On the Structure and Origin of certain Rocks of the Laurentian System. 

 By Frank D. Adams, Ph.D., F.R.S.C., McGill University, Montreal. 



The paper presents the results of recent and somewhat extended studies of 

 several areas of the Laurentian of Canada, and deals more particularly with the 

 origin of certain members of this system as indicated by their structure or com- 

 position. While it is impossible in the present state of our knowledge to arrive at 

 any definite conclusions concerning the origin of many, or perhaps even of the 

 majority, of the rocks composing the Laurentian, the origin of certain members of 

 the system can be determined. Some of these, although now possessing a more or 

 less distinct and even highly pronounced foliation or stratiform appearance, can be 

 proved to be igneous or intrusive rocks, while it can be shown that others are of 

 aqueous origin. 



To the former class belong the anorthosites and many of the orthoclase 

 gneisses. These rocks, although frequently distinctly foliated, can in many places- 

 be traced into perfectly massive varieties, and form great intrusions, interrupting- 

 and cutting off" the older members of the system. The foliation and stratiform 

 appearance which led the older geologists to class them as altered sediments is due- 

 to movements induced by pressure, and they show protoclastic or cataclastic 

 structure in great perfection. 



To the aqueous rocks, on the other hand, belong the crystalhne limestones and 

 certain gneisses usuaUy associated with them. These rocks not only differ in 

 structure from those above referred to, but have a chemical composition not 

 possessed by any igneous rock. The cataclastic structures are very subordinate, 

 and the rocks are characterised by a very extensive recrystallisation, accompanied 

 by the development of new minerals. 



It may therefore be said, without going beyond that which the facts warrant,, 

 that there are in the Laurentian at least two distinct sets of foliated rocks. One 

 of these, comprising the limestones, some quartzites, and certain garnetiferous or 

 sillimanite gneisses, represents, in all probability, highly altered and extremely 



