June 25, 1920] 



SCIENCE 



635 



of its former existence is preserved to us by 

 means of impressions, molds or casts. On the 

 other hand, certain shells preserved in the 

 Pre-Pleistocene formations and which are not 

 only practically unaltered but also have living 

 representatives, are true fossils. The element 

 of time as here applied to the definition may 

 seem to certain biologists and geologists to be 

 unessential. It is necessary, however, to have 

 some term which may be applied to the 

 "medals of creation" to set them apart from 

 the realm of organisms which are living, or 

 have lived within historic time. 



Fossils may be briefly classified as follows: 

 A. Direct evidence. 



1. Actual remains (spore cases; Oligocene 



ants, etc.). 



(a) Hard and soft parts preserved. 



(h) Hard parts only preserved. 



(c) Hard parts minus organic matter. 



(d) Hard parts plus mineral salts 



grading into : 



2. Minute replacements (coal balls; lab- 

 yrinthodont, teeth, etc.). 



Replacement molecule by molecule of 

 the original organic matter by min- 

 eral salts, resulting in petrifaction 

 which may or may not show struc- 

 ture. Results of metasomatic proe- 



We may smile when the novelist uses the 

 adjective, fossil, in a broad way; we may 

 even argue with the petrologist, or physiogra- 

 pher when he uses the term to describe in- 

 organic phenomena, but what are we to do 

 when the paleontologist speaks of "fossil 

 ripple-mark"? Clearly the word is rapidly 

 becoming so used that it will soon be useless 

 in a scientific sense. Since the paleontologist 

 is more interested in fossils than the petrog- 

 rapher, geographer or even the "general" 

 geologist, and since he alone has defined what 

 fossils are, is it too much for him to ask his 

 brother geologists to either adopt his defi- 

 nition or else to coin a new term which will 

 better express the antiquity of inorganic 

 structures. Perhaps it would be well for the 

 paleontologists to set an example in the 

 " good use " of the term, by using it correctly 

 themselves. As they are also vitally inter- 

 ested in the geologic time-table, perhaps it 

 would not be out of place for them to sug- 

 gest that Paleozoic, Mesozoic, or Tertiary pre- 

 fixed to " ripple-mark " or volcanoes would be 

 much more descriptive and accurate than the 

 adjective fossil. 



Richard M. Field 



Department op Geology, 

 Beown TJniveesity 



3. Coarse replacements (bulk of Palezoic 

 fossils) . 



(a) Molds of the exterior and in- 

 terior. 

 (h) Casts of the exterior and inter- 

 mediate structures. 

 4. Prints (leaves; jelly fish, etc.). Plus 

 or minus organic matter in the case 

 of plants. 

 B. Indirect evidence. 



1. Coprolites. 



(a) Whole or part of original sub- 

 stance. 



(h) Casts of original substance (eoj)- 

 rolites of dinosaurs). 



2. Artifacts (ant hills; prehistoric flints, 



etc.). 



3. Tracks, trails or burrows (Arthro- 



phycus; dinosaur tracks, etc.). 



THE FIXATION OF ATMOSPHERIC NITROGEN 



To THE Editor of Science: Allow me 

 through the columns of Science to give pub- 

 licity to a most unique experiment related to 

 me by the late Dr. Paul Heroult, the in- 

 ventor of the electric steel furnace, and 

 simultaneously with Hall of the electrolytic 

 process for the isolation of aluminmn. 



It serves to show in a simple but striking 

 way the " fixation of atmospheric nitrogen " of 

 which we have heard so much in the past 

 four years. 



Although described and shown to many sci- 

 entific friends it was new to them all, and as 

 it lends itself to lecture demonstration de- 

 serves to be better knowu. 



The experiment consists in thoroughly mix- 

 ing 90 grams of fine aluminum powder with 

 10 grams of lamp-black. This mixture is 



