Geologic Correlation.— Ward. 57 
The celebrated case of the beds of Chardonet, department of 
Hanutes-Alpes, studied by Elie de Beaumontin 1828, and positively 
referred to the Mesozoic, but in which fossil plants of the genera 
Calamites, Sigillaria, and Lepidodendron were identified by 
Brongniart, is one of the best illustrations of this principle. 
And although, so young was the science of paleobotany at that 
time, that Brongniart himself was inclined to admit that these 
genera might occur in the Mesozoic, still, long before his death 
this was known to be impossible, and no paleobotanist would now 
hesitate in a similar case to tell the geologist that he had cer- 
tainly made a mistake in his stratigraphy. 
But in the determination of nearly related strata this is not 
possible, and limited material or single fragmentary specimens 
are not adequate. For such cases in order to be certain it is 
necessary to have a body of facts; in other words a fair series of 
good specimens of fossil plants is required before the paleobotan- 
ist ought to attempt to express his opinion with regard to the 
exact age of the deposit in which they are found. Most of the 
serious mistakes which have been made, and which have gone far 
to bring the science of paleobotany into disrepute, have resulted 
from neglecting this principle. Purely stratigraphical geologists 
have no conception of these laws, and a paleobotanist has to deal 
with them very much as he would deal with the notions of un- 
scientific persons. They are constantly bringing him mere frag- 
ments and only isolated specimens, not perhaps specifically de- 
terminable, and they expect of him that from such material he 
will be able to tell them the exact age to which it belongs. This 
is simply impossible, and the paleobotanist who will base definite 
conclusions upon such material is certain to err. 
On the other hand, where such a sufficient body of facts exists 
paleobotany becomes as conclusive for more nearly related forma- 
tions as for more widely separated ones. As an_ illustration of 
this, take the clays of Gay Head, Massachusetts. There is no 
spot more tempting to the stratigraphical geologist in this coun- 
try than Gay Head. Beautifully stratified clays of varied hues 
marking the dip and always freshly worn, form a precipitous cliff 
visible as a gayly colored object from great distances at sea’; and 
about the first work that geologists did in America was to attack 
the problem of the age of this cliff. The records’ of this work 
date back one hundred yews, and the names of the most eminent 
