184 Report of the State Geologist. 



ancient one, to discover at what epoch and by what process the 

 distinct groups, between which passage forms are wanting in 

 living nature, came into existence. It will be understood that 

 when the question concerns the establishing of relationships 

 between genera and families, and especially between species of 

 the same group, such a study can only be entered on with some 

 chance of success, when the materials for comparison are very 

 abundant, when they come from numerous localities and are in 

 a good state of preservation. 



For a group where any one of these conditions is wanting, it 

 would be illusory to seek to draw from the stratigraphic succes- 

 sion conclusions of phylogenetic order. This, for example, is 

 the case for the Crinoids. These Echinoderms are abundant 

 only in very few regions, and it is improbable that they were 

 everywhere evolved on the spot. For the Ammonites, on the 

 contrary, the method of which we are speaking, combined intelli- 

 gently with the preceding two, has already succeeded in giving 

 interesting results, for the specimens collected up to the present 

 are innumerable and gathered from all parts of the world ; 

 moreover, they can be collected any day, as many as are desired 

 for any especial object. The Echini also are common fossils and 

 present numerous characteristics which can be utilized for afl&li- 

 ation. M. Munier-Chalmas has for many years followed step by 

 step their evolution, and has made a study of all the terms of 

 transition which have come under his observation. He has seen 

 that sometimes continuous modifications can be followed through 

 a long series of forms, while the heads of certain series appear 

 suddenly, making it impossible to form any judgment as to their 

 origin except a hypothetic one. On these points of strati- 

 graphic and morphologic discontinuity, he established the great 

 divisions of his classification. The result of these researches, 

 which have not yet been published, we are authorized to present 

 in the chapter which treats of the classification of these animals. 



Continuity is then our principal guide in synthetic researches 

 of this kind. Unfortunately in a great number of cases the 

 evidence to be had is not sufficient to warrant the attempt to apply 

 this principle. We have seen in the preceding chapter, that in 

 consequence of the very progress of the phenomena, we shall 

 never possess the intermediates between all the species. 



