1885.] Geology and Paleontology. ; 165 
ported great distances during the Pleistocene period. There are 
several localities in the District of Columbia where such boulders 
may be seen, but their development cannot be studied so well as 
in the artificial cuttings in the hillsides along the Potomac river. 
aving made a study of these large boulders in a state of 
formation, one, who is familiar with Northern erratics, is led to 
agree with Dr. Sterry Hunt, that at least the larger “rounded 
masses of crystalline rocks, left in the process of decay, consti- 
tute the boulders of the drift,’ and not only these but many 
roches moutonnées. 
his deduction has been objected to upon the ground that 
boulders generally do not continue to enfoliate. 
n the District of Columbia many of the boulders seen out ot 
the hillsides described, do not show continued exfoliation (natu- 
rally very slow and with the atmospheric forces removing such as 
rapidly as formed, where not protected) any more than many 
erratics, while others are more or less uniformly OT through- 
out the whole mass. 
Although very many erratics do not show regula exfoliation, 
yet there are numbers of places where exfoliating boulders may 
be found in the drift. Perhaps there are no better localities for 
studying these rocks than those I examined during the last two 
summers, in the greater drift deposits along the Mississippi river, 
at Burlington, Keokuk, Warsaw and elsewhere. At these places 
numerous northern boulders—mostly greenstones—may be found 
_ Of various sizes from a few pounds to a few thousand, which are 
now exfoliating and in various stages of decay, having forms 
from subangular to spheroidal. Also near the southern limit of 
ee drift, at Columbia, Mo., situated upon the highlands, away 
m the river valleys, similar examples may be found, both of 
pheeiikeitie and gneissoid rocks. 
Neither the presence nor absence of ice scratches affect the 
above explanation of the primary origin of these large boulders, 
but only represent subsequent abrasion, or the absence of that 
action, or else the more recent surface decay of the rocks them- 
selves. —J. W. Spencer, M.A., Ph.D., F.G.S. 
ARE THERE ANY FOSSIL ALGa ?—Mr. Lester F. Ward, in a 
paper read before the American Association at Philadelphia gave. 
some statistics of the fossil flora of the globe. Among other 
things he said that from the Lower Silurian there have been de- 
scribed species of Algæ. The question arises, what are the prob- 
abilities of Algæ being preserved in a fossil state ? 
It seems to have been the habit of geologists, almost from the 
time that palæontology assumed: the aspect of a science, to 
refer to “fucoids” or Alge many fossil markings which were 
evidently not animal remains. It was assumed that everything 
fossil must have been an organism, and it is only of late years 
