ON OOLITES AND SPHERULITES . 607 
tions of organic fragments by the interlacing tubes of Girvanella 
and should therefore not be called odlites at all* When exposed, 
true odlites may, of course, be incrusted in the same way. 
SOURCES OF ERROR IN INTERPRETING ORIGIN OF OOLITES 
Secondarily deposited odlites.—Erroneous conceptions concerning 
the origin of odlites may arise if no clear distinction is made between 
layers in which the odlitic grains are found zm situ and such in which 
they were redeposited after transportation. The secondary origin 
of odlitic deposits may be recognized by the practical absence of a 
matrix, by the uniformity of size of grains (indicating sorting), by 
cross-bedding, or by the presence of substances accidentally en- 
meshed in the odlitic grains which are foreign to the surrounding 
matrix, etc. In such cases the odlitic grains were either washed 
by waves or currents from their place of origin and redeposited in 
water, or they were carried inland by the wind where they may have 
formed dunes, as they do now on the shores of the Red Sea and of 
Great Salt Lake.? The recognition of such secondary odlites and 
their correlation with synchronous primary deposits may, under some 
circumstances, convey valuable information to the paleogeographer. 
It is often quite difficult to prove satisfactorily the origin 27 sztu 
of an odlite. For this we must, in many cases, rely entirely on a 
microscopic study of the relation existing between the matrix and 
the odlitic grains. In some cases, however, the characteristic 
incrustations and massive growths, called ‘‘stromatoliths” by 
Kalkowsky,’ are found associated with the odlitic grains and by 
their presence prove the primary nature of the odlites, as, for 
instance, in the Upper Triassic (Rhaetic) of England, the Mississip- 
pian of Belgium, the Lower Bunter of Northwestern Germany, 
the Tertiary of the Rhine Valley, etc.‘ 
t The term “‘pseudodlite” has been used for grains imitating odlites; for instance, 
minute pellets of dense limestone in a limestone matrix (cf. O. M. Reis, Geognostische 
Jahreshefte, XXII [1909], 228). 
2J. Walther, Lithogenesis der Gegenwart (Jena, 1894), pp. 659, 690, 8490; A. W. 
Grabau, Principles of Stratigraphy (New York, 1913), pp. 468, 472. 
3 Kalkowsky, Monatsber. Deutsch. geol. Ges., LX, I (1908), 68-125. 
4 Cf. O. Reis, “‘Ueber Stromatolith und Oolith,” N. Jahrb. fiir Min., etc. (1908) 
Part II, pp. 114-38. 
