of Grinnell Land and North Greenland. 485 



surmounted by beds of gravel. The fine muds and sands must 

 have been deposited in salt water, as is shown by the numerous 

 molluscan remains they contain ; w^iilst the superincumbent 

 unfossiliferous gravels must have been deposited by the 

 streams on the top of the mud beds as the land rose ; for the 

 finest material would naturally be borne furthest seaward. 

 Had there been periods of subsidence, we should undoubtedly 

 find the mud and gravel beds intercalating. During upheaval 

 the gravel beds would be deposited, as we find them, above the 

 sands ; if periods of subsidence had intervened, mud and sand 

 beds would have been found above the gravels. 



The formation of the lakes is obvious. As a bay silts up, 

 and the depth of water at its mouth lessens, the heavy floe 

 Iriven in from seaward grounds ; the almost irresistible pres- 

 sure of the polar pack exerted on the floebergs buries tliera 

 deep in the yielding material, which is at the same time 

 forced up into a bar. The process of upheaval continues ; the 

 bay becomes a lake ; the embankment is soon cut through by 

 the water that seeks an outlet from the lake in summer ; the 

 waters of the lake are lowered, and wide margins of mud are 

 exposed. These are frozen and snow-covered for ten months 

 of the year, except where the gales of wind have scooped out 

 the snow and left the ground exposed but frozen as hard 

 as any rock. During the brief summer, when the borders of 

 the lake are exposed, they have the appearance as if the tide 

 had only lately receded ; the shells of Alya truncata^ Saxicaoa 

 rugosa, and Astarte borealis are strewed around in great pro- 

 fusion, with large quantities of drift-wood, and in some few 

 instances mammalian remains. 



Oscillations of level in these regions since the close of the 

 Tertiary epoch must have occurred on a considerable scale ; 

 for I detected Post-tertiary beds resting on undoubted Mio- 

 cene strata, and extending to an elevation of not less than 

 1000 feet above their level. The obvious conclusion is, that 

 since the period when a flora analogous in some respects 

 to that now existing in Mexico flourished within 500 miles 

 of the northern axis of our planet, there has been a subsidence 

 of over 1000 feet, and a subsequent upheaval to a similar 

 altitude. 



I have thus alluded briefly to the geological structure of 

 these Post-tertiary deposits, in the hope of making the descrip- 

 tion of the different stations referred to hereafter intelligible 

 to the reader. The stations numbered and described in the 

 following notes are additional to tiiose recorded by Dr. Gwyn 

 Jeffreys* : — 



* Antca, p. 231. 



