55 o POPULAR SCIENCE MONTHLY. 



are of a permanent character, begin with a broad foundation of ob- 

 servation. The work that begins with theory and afterward seeks 

 for verification through observation may be brilliant and attractive, 

 but its results are rarely of lasting value. Mr. Walcott' s scientific 

 work has followed the normal and conservative course, beginning 

 with the prolonged collection of specimens and other facts, following 

 with generalization, chiefly in the field of the correlation of forma- 

 tions, and leaving largely to the future conclusions as to sequence 

 and genesis. 



His paleontological studies have been of two classes: biological, 

 viewing fossil organisms as members of the animal kingdom, and 

 stratigraphical, viewing associated fossils or faunas as the representa- 

 tives of contemporaneous life and the labels of synchronous forma- 

 tions. His biological labors include the description of a considerable 

 number of new families, genera, and species of Palaeozoic inverte- 

 brates, and an elaborate study of the structure and organization of 

 trilobites, which has served to give them, for the first time, a definite 

 and unquestioned position in the systematic scheme of animal forms. 



The trilobites were dominant forms in early Palaeozoic time, and 

 continued, with diminishing numbers and importance, until the Car- 

 boniferous period. Exhibiting a considerable range of differentia- 

 tion, they have been of great service for the classification of terranes, 

 and the nomenclature of the Cambrian horizons has been based upon 

 them. Nevertheless, their systematic affinities were long in doubt, 

 because they were known only through imperfect specimens, exhibit- 

 ing the dorsal armor, but showing no trace of appendages for locomo- 

 tion, respiration, etc. From time to time the discovery of legs and 

 other members had been announced and subsequently disproved, and 

 geologists had become so skeptical as to the possibility of their deter- 

 mination that when traces of a leg were actually discovered by E. 

 Billings, in 1870, little credit was given to the announcement. Here 

 was an important biological blank to be filled, and Mr. "Walcott, at 

 the suggestion of Louis Agassiz, undertook to fill it. The examina- 

 tion of thousands of trilobite specimens perfect as to the carapace 

 revealed but a few traces of organs, and it was found that those 

 traces all came from a certain layer of Trenton limestone only a 

 few inches in thickness. That layer was carefully quarried over a 

 considerable area, even though it became necessary to remove sev- 

 ral feet of superjacent strata. Several thousand complete tests were 

 obtained from it, and two hundred and seventy of these were found 

 to contain some of the missing members in greater or less perfection. 

 To such specimens elaborate study was given, chiefly by means of 

 translucent thin sections, such as are employed by the petrographer. 

 With their aid, and through prolonged labor and study, Mr. Walcott 



