42 REPORT OF THE SECRETARY. 



condition. But it is not sufficient for the full investigation of the 

 subject to provide the means of studying the living faunas and floras 

 •which now characterize different districts ; — science also requires the 

 collection of materials for the investigation of the animal and vegetable 

 forms which existed at the same and different localities at various 

 epochs in the past history of the globe, or, in other words, it is de- 

 sirous to obtain data for the investigation of the phenomena of life, as 

 it is exhibited in time as well as in space ; and hence attention is also 

 given to the collection of complete suites of the organic remains, par- 

 ticularly of the hitherto unexplored parts of this country. 



In reference to the solution of some important questions now pend- 

 ing in relation to natural history, Professor Agassiz has called our atten- 

 tion to several special collections, and as his suggestions are of general 

 interest, I will here mention them. First, he commends to attention 

 the tertiary shells, on account of their bearing on the problem of the 

 mean annual temperature of the globe at different periods anterior to 

 its present geological condition. Different species of these animals exist 

 at present each in water of a given temperature ; and by ascertaining 

 the temperature congenial to each species from actual observation on 

 different parts of the coast, a thermometrical scale would be given by 

 which to determine the climate of any place in the past geological 

 periods in which these animals existed. The United States is most 

 favorably situated for the solution of this question. Its eastern coast 

 extends north and south over more than 23 degrees of latitude, along 

 which shells are everywhere common, and present remarkable changes 

 in their distribution and mode of association. A large collection of 

 these fossil shells from the tertiary beds in different latitudes from 

 Maine to Georgia, properly arranged, would, in time, afford as precise 

 data for ascertaining the mean annual temperature of these shores 

 during the different periods of the tertiary times as an actual series of 

 instrumental observations. 



Another collection to which the same distinguished naturalist has 

 called our attention is a series of embryos and young animals of 

 different species. It is a well established fact that animals of a higher 

 type pass from the first inception of life in the embryonic state 

 through a series of forms resembling the lower animals, so that even 

 in the case of man himself the embryo assumes the form of the fish 

 or the reptile. The study, therefore, of a series of animals, selected 

 at different periods of gestation, is of the highest importance in tracing 

 the progress of their separate developments, and also of ascertaining 

 the probable forms under which organized beings may be exhibited in 

 different parts of the present, or in the remains of the past ages of the 



