HORNBEAM, HAZEL, BIRCH AND ALDER 105 



Hazel leaves are broadly ovate, with sharply pointed tips and 

 truncate or heart shaped bases. The margins are finely toothed and 

 may be in addition cut into small segments, suggestive of the leaves 

 of the white birch, but coarser and of a different shade of green. 

 The leaves of all the species have a great mutual resemblance 

 and show considerable variability, so that it becomes exceedingly 

 difiicult to discriminate the fossil species, which consequently have 

 been multiplied beyond all reason. 



Scarcely any of our trees are more interesting in that hazel 

 leaves are very common as fossils in northern lands beyond their 

 present limits, and have the distinction of having been found to 

 within 10° or 12° of the pole, being consequently of much impor- 

 tance in attempts to picture Tertiary geological climates. 



Conservatively treated the number of extinct kinds of hazel 

 considerably exceeds the living varieties, and the more spectacular 

 time in their history was at the time of their earliest appearance 

 in the geological record. This was during the early Tertiary, for 

 none are known from the Upper Cretaceous. About 10 species 

 are known from this early Tertiary or Eocene time, and 2 of these, 

 found in the wooded region that at that time covered our prairie 

 country in western Canada, the Dakotas, Montana, etc., are so 

 Hke our two existing Atlantic species that their leaves are scarcely 

 to be distinguished and have frequently gone by the same names, 

 although of course no tree species has continued unaltered through 

 such a vast lapse of time as that separating the Eocene from the 

 present. 



But the chief interest of the Eocene hazels is their northern 

 range. They were exceedingly abundant at that time in the far 

 northern parts of all the continents of the Northern Hemisphere. 

 At least 3 species and many varieties are found in Alaska, where 

 their leaves are among the commonest of fossils. If the Macken- 

 zie River existed in those far off days, hazel thickets hned its bank 

 where it emptied into the Arctic Ocean since their fossil remains 

 are common in the shales near its mouth. Hazels were equally 

 common in western Greenland and between the early Tertiary 

 lava flows on the Island of Mull, and in Siberia. Still farther north 



