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THE POPULAR SCIENCE MONTHLY. 



there has been in connection with the Glacial 

 period a succession of oscillations of the 

 earth's crust nearly duplicating one another. 

 Such oscillations seem to have occurred in 

 various geological ages, as, for instance, dur- 

 ing the coal period, when the successive coal 

 beds were formed. And, indeed, much can 

 be said in favor of the view that such an 

 oscillation when once begun would perpetu- 

 ate itself. . . . But our knowledge of these 

 matters is too vague to reason of it with any 

 confidence, as is that also of the other causes 

 which have been suggested for the produc- 

 tion of the phenomena of the period. In 

 conclusion, it is sufficient to remark that our 

 present state of knowledge on the subject 

 seems so imperfect that it is not conducive 

 to success in investigation to hold any theory 

 as to the unity or duality of the period with 

 great positiveness. Overconfidence on this 

 point at the present time is likely to blind 

 the eyes of the investigator, and to hinder 

 progress both in the collection and in the in- 

 terpretation of the multitudinous and com- 

 plicated facts which everywhere invite our 

 close attention." 



Preservation of Leaves as Fossils. — In 



a paper on the Preservation of Plants as Fos- 

 sils, Mr. Joseph F. James, of Cincinnati, 

 names as one of the requisites to secure the 

 preservation of any plant, that it must be in 

 a position to be almost immediately covered 

 by some material. A leaf or branch falling 

 to the ground and likely to be exposed to 

 the elements has a poor prospect of being 

 preserved. But if it fall into the water and, 

 sinking to the bottom of a lake or swamp or 

 morass, be covered by mud or sand ; or if it 

 He on the seashore and be covered by sand 

 brought in with the tide, it may at least leave 

 its mark. Or it may, through certain chem- 

 ical properties it possesses, so act upon the 

 stone on which it lies as to be preserved, not 

 in actual substance, but as an intaglio. The 

 author was impressed with the possibilities 

 of the last process while walking along the 

 street in the rain and looking at the fallen 

 leaves on the pavements. He first noticed 

 numerous irregular, discolored patches on 

 the stone slabs. Looking more closely, he 

 says : " I found that these discolorations had 

 been caused by the leaves, which had left 

 their impress on the stone. In many cases 



this impression was so distinct that there 

 was no difficulty in recognizing the species. 

 The leaves were those of the soft maple, one 

 or two species of oak, tulip tree, and syca- 

 more. There is here a possibility of the 

 preservation of the remains of plants, or, at 

 all events, of their impress upon stone, had 

 it occurred under more favorable circum- 

 stances. But on a pavement, where people 

 were passing constantly, the impressions were 

 worn off and soon disappeared. The rain, 

 however, did not seem to wash them away, 

 so they were something more than mere sur- 

 face markings." A similar phenomenon was 

 observed and described in 1858 by Mr. Charles 

 Peach in a paper on the Nature Printing of 

 Sea-weeds, on the rocks of one of the Ork- 

 ney Islands in Scotland. 



Breath Figures. — Some interesting ex- 

 periments are described by W. B. Croft in 

 the production of " breath figures " — or la- 

 tent impressions on contact of objects with 

 glass and electrifying, which are made visi- 

 ble by breathing upon them. While there 

 appears to be no limit to the durability of 

 these figures if they are carefully protected, 

 they usually become obscured by dust gath- 

 ering on them after being often breathed 

 upon. But certain changes or developments 

 take place after the lapse of some weeks or 

 months. In coin pictures, the object is near 

 to the glass, but not in contact with it ; for 

 in the best specimens the rim of the coin 

 keeps the inner part clear of the surface. 

 Even if a coin only rest for a while on glass, 

 an outline of the disk and sometimes faint 

 traces of the inner detail will be produced 

 when the spot is breathed upon. An exami- 

 nation paper, printed on one side, put be- 

 tween two plates of glass and left for ten 

 hours, either in the dark or the daylight, will 

 leave a perfect breath impression of tbe print, 

 both on the glass that lay against the print, 

 and on that which faced the blank side of 

 the paper. Sometimes both impressions are 

 white, and sometimes they are both black ; 

 or one may be part white and part black, or 

 may even change while being examined. The 

 impressions were very easy to produce during 

 a sharp frost with east winds early in March, 

 1890. The following experiments easily suc- 

 ceed at any time : Stars and crosses of paper 

 are placed for a few hours beneath a plate of 



