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themselves, or upon their own axes, he has endeavoured to show 

 that, whether the cleavage-cut strata have been much disturbed or 

 not, the cleavage planes invariably approximate to parallelism with 

 those great planes in the crust, which give indications of having been 

 the planes of maximum temperature. It has been already stated, in 

 the present paper, that the cleavage dip is parallel to the average 

 dip of the anticlinal and synclinal axis planes bisecting the flexures. 

 Now it is easy to prove that these axis planes, and the inverted parts 

 of the flexures, are just those portions where the greatest crushing, 

 Assuring, and displacement of the strata must have occurred, and 

 where the highly heated pent-up volcanic steam, gases, and liquid 

 mineral matter would find their chief channels obliquely upward to- 

 wards the surface. Not to attempt the application of this view in 

 detail, it will suffice at present to state, that every plicated belt of 

 strata may be regarded as having, at the time of its folding and 

 metamorphism, contained from this cause a series of alternate hotter 

 and colder planes or belts, arranged in parallel oblique dip. These 

 planes of temperature are supposed to have acted to polarize the 

 particles of the strata in corresponding parallel planes, by transmit- 

 ting through the half-softened mass parallel waves of heat, stimu- 

 lating the molecular crystalline forces ever resident in mineral mat- 

 ter in planes parallel to the generating surfaces. 



3. On a Property of Numbers. By Balfour Stewart, Esq. 

 Communicated by Professor Kelland. 



4. Analysis of Craigleith Sandstone. By Thomas Bloxam, 

 Esq., Assistant-Chemist, Industrial Museum, with a Pre- 

 liminary Note by Professor George Wilson. 



One object of the Laboratory of the Industrial Museum is the pro- 

 secution of investigations likely to throw light on the economic value 

 of materials employed in the useful arts. It has been impossible 

 this winter to do more than make a small beginning by instituting 

 an examination into the properties of certain of our building stones ; 

 and as the results obtained in the case of the sandstone of Craigleith 

 Quarry have an interest for geologists as well as for architects and 

 builders, they are laid before the Society, as all similar results of any 



