Americaii Association. 255 



mound. This same effect upon frozen earth had caused in some 

 places during the past winter the cracking of the ground with 

 loud reports, which had alarmed people in the vicinity." 



Some discussion ensued as to the hollowness of the crystal 

 which did not seem satisfactorily accounted for. It was suggested, 

 however, that the enclosed water must have found means^of es- 

 cape ere the solidification was complete. 



We close our brief and imperfect notice of the Physical section. 

 with two papers by Prof. Smallwood. One of these related 

 to that mysterious substance, or probably modification of the 

 oxygen of the atmosphere. Ozone. The other' was an inte- 

 resting account of the Meteorology of Montreal and its 

 ViciNiTV These papers we do not at present notice more at 

 length, as we hope to have the papers themselves for publication. 



SECTION OF NATURAL HISTORY AND GEOLOGY. 



The first paper in this section, by Mr. Snell, described some 

 processes for the quantitative assay of chromium by the blowpipe. 

 The next was that on Sternhergia^ by Prof. Dawson, which we pub- 

 lish in the present number. Mr. Lesley then read a description of 

 some curious Flexures of the strata, in the Broad-top coal 

 field of Pennsylvania, which he attributed to enormous lateral 

 pressure acting on soft beds, compressed between sheets of inflex- 

 ible sandstone. The results, as exhibited by Mr. Lesley, from 

 actual measurements, are very singular, and most perplexing to the 

 miner and geological observer. 



Sir "W". E. Logan then read a paper explanatory of the destinc- 

 tion between the great series of ancient metamorphio rocks 

 which he had named respectively the 



HURONIAN AND LAURENTIAN SERIES OF CANADA. 



" The sub-silurian azoic rocks of Canada occupy an area of 

 nearly a-quarter of a million of square miles. Independent of 

 their stratification, the parallelism that can be shown to exist 

 between their lithological character and that of metamorphic 

 rocks of a later age, leaves no doubt in my mind that they are a 

 series of very ancient sedimentary deposits in an altered condition. 

 The further they are investigated, the greater is the evidence that 

 they must be of very great thickness, and the more strongly is the 

 conviction forced upon me that they are capable of division into 



