O. A. White — Puget Group of Washington Territory. 449 



nearly fresh as to afford a congenial habitat for such a mollus- 

 can fauna as it is known to have possessed, and as was necessary 

 for the accumulation of the great thickness of strata in which 

 the remains of that fauna are found, during so long a period 

 of time. 



That is, it is difficult to understand how that comparatively 

 narrow portion of the continent between the then existing 

 Laramie hydrographic basin on the east, and the Puget estuary 

 on the west could have furnished a sufficient flow of fluviatile 

 water to keep nearly fresh so large an estuary, and keep off the 

 encroachment of adjacent marine waters. Even so large a flow 

 as is now discharged by the Columbia would seem to have been 

 insufficient unless the outlet of the great estuary was greatly 

 narrowed by land barriers. 



Again, the evidence presented by Mr. Willis, and also that 

 afforded by the fossils, which range without material change 

 through a large part of the vertical series, seems to be conclu- 

 sive that essentially uniform estuarine conditions were preserved 

 over the whole area now occupied by the Puget Group from 

 the time of the deposition of its earliest, to that of its latest 

 strata. This evidence also discloses the remarkable fact that 

 during that time there was a constant subsidence over the 

 whole area, until it had reached a maximum of not less than 

 twelve thousand feet. 



It is certainly difficult to understand how so great a subsi- 

 dence could have taken place without such a simultaneous ele- 

 vation of the adjacent land area as would have materially 

 changed the character and uniformity of the supply of fluvia- 

 tile waters to the estuary, or have added a land area to the 

 westward of it. Indeed, it is difficult to understand how even 

 a less subsidence could have taken place without materially 

 modifying the character of the great estuary itself, or even 

 submerging its whole area beneath marine waters. 



The biological relations of this Puget fauna to other faunas 

 possess peculiar interest. For purposes of comparison one in- 

 stinctively turns to the molluscan fauna of the Laramie Group ; 

 but in doing so important differences appear. It is true there 

 are two species of Corbicula in the Puget fauna that are so 

 closely like Laramie forms as to suggest specific identity upon 

 casual examination ; but the differences between the two faunas 

 are strikingly shown by the family and generic characters of 

 the other members of the Puget fauna as compared with the 

 Laramie fauna. 



For example, a species of Teredo has been found in the 

 Puget Group, but no member of the Teredinidse has yet been 

 found in the Laramie. Two species of the Puget fauna are 

 referred to the Tellinidae, but no member of that family has 



