— Geology. mee 435 
sketches made from incomplete specimens. Nevertheless, it is but right 
to remark in favor of the opinion of Dr. Heer that Populus Leuce has not 
the leaves toothed as Dr. Newberry says, but only subdenticulate, follow- 
ing Unger’s figure and description. Moreover, species of Populus bear 
toothed and entire leaves on the same branches. 
The third assertion, about the value of the genus Httingshausenia, con- 
cerns only the author of the genus and has nothing to do with the deter- 
mination of the species. There was no call for a critique upon Prof. Heer 
on this account. 
The fourth statement is the only essential one; it is: “that excepting 
the so-called Credneria and Ettingshausenia, all the genera enumerated in 
Dr. Newberry’s letter are Tertiary and not Cretaceous.” 
Nobody will consider as identical the genera Salicites and Salix, Al- 
nites and Alnus. Then, from the elevén genera enumerated by Dr. New- 
berry, two only are found in the list of Hiehle, containing seventeen. 
_ genera. These two genera are Populus and Acer, the true characteristic 
he of the tertiary of Europe. The first is represented already in that 
' ation by thirty-three species; the second by forty-five or more, an 
 &Xeept the species admitted by Hiehle, not a single one has been found | 
in the Cretaceous, From the nine other genera of Dr. Newberry which 
ate not mentioned as Cretaceous by Hiehle, not one-has been found by 
_ anybody else in that formation. Hence Prof. Heer was right to say that, 
except the two which he named, all the genera enumerated in the letter 
of Dr. Newberry were of the Tertiary and not of the Cretaceous, Every 
botanist without exception would have come to the same conclusion, 
_ therefore I cannot understand how the accusation of ignorance or of 
Inthe letter of Prof Heer, there is not a word which could be con- 
gone When the most ‘naught 
ts take in i jes and genera for re-examination, 
Ke again and again spec nt names, of relations, of on 
5 
F : t 
a psn rs Palzontology is scarcely born, 
