92 Marl of New Jersey. 
whiteness. Those who have seen it in the quarries, or noticed its 
vast masses not distinctly stratified, and separated. by beds of black 
flint, suppose these features essential to its external characters.” 
* . * * * 
_“ This idea, although tolerably correct, is not complete: fora long 
time its external and mineralogical characters were alone considered; 
while its geological features, or those which belong to the formations 
(terrains) it embraces have been almost entirely overlooked, as well 
by geologists as by naturalists in general. = 
* The difficulty does-not consist in recognizing beds of white chalk 
containing black flint, but in detecting those deposits which want these 
external characters, and yet belong to the same age and formation. 
ow we determine a formation (that is to say,-any combination of 
mineral substances which have been deposited at the same time,) by 
the position it occupies, relatively to the series which forms the crust 
of the globe; or in other words, by the kind of rocks or deposits 
which are constantly found above and below it: this is the geological 
character, or that of superposition, the most important of all when 
clearly ascertained. 
formation. 
“It will now be understood what we mean by a chalk formation, 
or rather by a cretaceous formation: we must not picture to ourselves 
deposits wholly composed of “white chalk ; but include in the desig- 
nation all those beds which occu: 
sometimes also presenting the same assemblage of mineralogical char- 
acters. We shall find cretaceous formations both black and yellow, 
en masse or stratified, with or without silex : we shall even see that 
these deposits are sometimes composed entirely of sand, and of sand- 
stone, without a particle of chalk, mineralogicall: ki ven 
of carbiiaiech.tme? 3 Deny eo 
