2 GIRTY 



amount and variety of the evidence which passed before me, 

 together with the pressure of other work, has prevented the 

 making of final comparisons and the developing of evidence 

 in such detail that conclusions could be said to be proved to 

 myself, or that they could be presented for the conviction of 

 others. 



Until this could be carried out I thought to refrain from pub- 

 lishing these observations ; but it has latterly seemed to me that 

 many of them are of sufficient interest and sufficiently well sub- 

 stantiated to make a statement desirable, even though my vie;ws 

 should subsequently need to be modified and though the presen- 

 tation of the evidence upon which they are based should prove to 

 be, as it clearly will, the work of years. It is partly on this 

 account, the necessity of choice between the early statement of 

 conclusions which are more or less tentative, and a delayed and 

 gradual presentation of better established ones, together with 

 the feeling that to formulate these views now might aid myself 

 as well as others in a more speedy arrival at the truth, by de- 

 termining what the objective really is, that the former course 

 has been chosen. 



Several years ago I studied and described in detail the fauna 

 of the Madison limestone of Yellowstone National Park.^ This 

 fauna proves to be characteristic of the Lower Carboniferous of 

 the Western States, in nearly every one of which it occurs, 

 locally modified perhaps, but retaining the same general expres- 

 sion, from the Canadian to the Mexican boundary and as far 

 west as Nevada. In California the fauna of the Baird shale, 

 which has generally been called Lower Carboniferous, is entirely 

 different, and while it has not yet been found in Washington or 

 Oregon, it seems probable that the areas of those States shared 

 the same geological and biological history during this period. 

 The Mississippian faunas of the Mississippi valley seem never 

 to have found entrance into this region, or, if so, whatev^er 

 traces have not been lost are thus far undiscovered. On the 

 other hand, it is uncertain if the California fauna ever pene- 

 trated into the region eastward. One of its most striking feat- 

 ures is a large Productus resembling P. gigantcus of the 



'U. S. Geol. Surv., Mon. No. 32, 1899, pt. 2, chap. 12, sec. 2. 



