152 Report of the State Geologist. 



nature everywhere seems to give an emphatic denial of the cele- 

 brated formula so long considered an axiom, natura non facit 

 saltus. The continuity is sometimes manifest, evident to the 

 point of rendering it almost impossible to form distinct groups, 

 for example, of those contained in a large genus ; but the interme- 

 diate forms are more and more rare between genera, families^ 

 orders and classes. There are times when evolution seems to 

 have proceeded by leaps more and more abrupt. There is a 

 much greater difference between the Acephalate and the Gaster- 

 opod which resembles it the most closely, than there is between 

 the two extremes of the series of. Acephala, or between the two 

 extremes of the series of Gasteropoda. Between the Reptiles and 

 Mammals only two or three intermediate forms are found, and 

 these are doubtful and aberrant. But if the appearance of this 

 last type had been as gradual as its. ulterior evolution, millions of 

 transition forms must have existed in a long series of geologic 

 beds, and it would have been impossible for them to have left 

 so few traces. 



A great majority of the transformist school of the present day 

 interpret these important facts by admitting that evolution must 

 have taken place sometimes very rapidly ; this is the hypothe- 

 sis of Saltation^ especially maintained by Cope and Haldeman. 

 It is incontrovertible that the rapi;lity of evolution in the same 

 group presents extreme variations ; thus, on the one side we see 

 the type of Lingnla existing without any important modification 

 from the Cambrian [Ordovician] epoch to the present, while among 

 the Terebratulas and Rhynchonellas the species is constantly 

 losing its hearings, as Yilmorin has picturesquely expressed it. It 

 is well known also that the essays of experimental transformism 

 have demonstrated that very appreciable variations can be ob- 

 tained in the course of a few generations. Saltation consists in 

 this, that these rapid variations of a given type may be continu- 

 ously produced in one and the same direction, so as to effect a 

 notable modification of the primitive type. There must have 

 been, in some sort, an accumulation of " progressive forces " and 

 the ^' conservative forces " yielding suddenly, finally permitted the 

 production of the evolution, for which preparation had been 

 made during the coarse of generations. This idea of the discon- 

 tinuity of the effect despite the continuity of the effort has 

 abundant illustration in all the physical sciences. 



