XX REPORT UNITED STATES GEOLOGICAL SURVEY. 



on this subject, which will eventually form one of the series of the quarto 

 Eeports of the Survey. 



The rhizopods are the lowest and simplest forms of animals, mostly- 

 minute, and requiring high power of the microscope to distinguish their 

 structure. While most of them construct shells of great beauty and 

 variety, their soft part consists of a jelly-like substance. This the ani- 

 mal has the power of extending in threads or finger-like processes, which 

 are used as organs of commotion and prehension, often branching. 

 From the appearance of their temporary organs, resembling roots, the 

 class of animals has received its name of rhizopoda, meaning literally 

 root-footed. 



In compensation for the smallness of these creatures, they make up 

 in numbers, and it is questionable whether any other class of animals 

 exceed them in importance in the economy of nature. Geological evi- 

 dence shows that they were the starting-point of animal life in time, and 

 their agency in rock-making has not been exceeded by later higher and 

 more visible forms. 



With the marine kind, known as foranlinifera, we have been longest 

 familiar, The beautiful many-chambered shells of these — for the most 

 part just visible to the naked eye — form a large portion of the ocean- 

 mud and the sands of the ocean-shore. Shells of foraminifera likewise 

 form the basis of miles of strata of limestone, such as the chalk of En- 

 gland and the limestones of which Paris and the pyramids of Egypt are 

 built. 



Fresh- water rhizopods, though not so abundant as marine forms, are 

 nevertheless very numerous. They mainly inhabit our lakes, ponds, and 

 standing waters, but they also swarm in sphagnous swamps, and ever 

 live in newest earth. Professor Leidy has devoted several years of 

 study to the fresh- water rhizopods of the eastern portion of our country, 

 and his especial object in the past expedition was to investigate those 

 which are to be found in the elevated regions of the Bocky Mountains. 



BOTANY. 



The botany of the Survey was represented the past season by the two 

 great masters of that department, Sir Joseph D. Hooker, director of the 

 G-ardens of Kew, England, and president of the Eoyal Society of Lon- 

 don ; and Prof. Asa Gray, of Cambridge, Mass. Their examinations ex- 

 tended over a great portion of Colorado, Wyoming, Utah, Nevada, and 

 California. Their investigation into the alpine floras and tree vegeta- 

 tion of the Eocky Mountains and Sierra Nevada enabled them to give a 

 clear idea of the relations and influence of the climatic conditions on 

 both sides of the great mountain-ranges. 



Sir Joseph Hooker, whose botanical researches embrace the greater 

 part of Europe -, the Indies, from the bay of Bengal across the Hima- 

 layas to Thibet ; the Antarctic regions and the southern part of South 

 America, New Zealand, Australia, South Africa, Morocco, and Asia 



