528 



THE AMERICAN NATURALIST 



[Vol. XL 



as arc affected by, or are coordinated witli tlie manner of progres- 

 sion. In the first of these pa])ers an atteni])t is made to cUi.ssifv 

 different series of footprints accordiiiir as tliey were made hy the ani- 

 mal in a resting posture, walking, or rutmiiig; in the second, argu- 

 ments are advanced to show that certain Dinosaurs are primarily 

 quadrupedal in gait, others secondarily so, as the result of change 

 in function amongst forms which reseml)led Iguanodon in being 

 primarily bipedal. The arguments are based upon persistence 



sources. Dollo's interpretation of tracks suggests the importance of 

 tracing as extended series of footprints matie by a single anitrud as we 

 can find record of in the Newark beds of the (\")nnecticut Vallev. 



C. R. E. 



GEOLOGY 



Ries's Economic Geology of the United States^ 



