1 20 (Review of Recent Geological Literahire.. 
westward to the Mississippi river, in central Minnesota, there is recog- 
nizable the following order of succession, beginning below: 
"(i) The great basement or Laurentian complex of gneiss, granite 
and crystalline schists; as to whose further divisibility no opinion is now 
offered. This is separated by a great discordance from 
"(2) The Huronian, a detrital iron-bearing series. A further discord- 
ance severs this from 
"(3) The Keweenaw an series of interleaved detrital and eruptive 
beds. This series again is entitled to the group rank. Above the Ke- 
weenaw series, and separated from it by yet a third great discordance, 
"(4) The Potsdam, or Upper Cambrian sandstone." 
Professor Irving proposes to limit the term Archzean to the crystal- 
line rocks below the Huronian. The Huronian and Keweenawan 
groups, together with any other groups now known, or hereafter discov- 
ered, to lie between Archaean and lower Palieozoic, or Cambrian, he 
would erect into a system, equivalent in rank to the Palaeozoic or Meso- 
zoic systems; and to this new system he proposes to apply the appropri- 
ate non-committal Agnotozoic, a term first proposed by president T. C. 
Chamberlin. 
Sand-honlders in the drift, or sith-aqiieons origin of the drift in central 
Missouri. By J. W. Spencer. (American Naturalist, vol. xxi, Octobei", 
1887.) This is the paper read by professor Spencer before the New 
York meeting of the American Association. The sand-boulders describ- 
ed were found in the surface deposits at Columbia, Missouri, within a 
few miles of the 39th parallel of latitude. Columbia is the seat of the 
state university of Missouri, and it was in making excavations for 
foundations of new buildings at the viniversity that sand-boulders were 
exposed. 
The sand-boulders arc masses of coarse sand, varying greatly in size, 
the largest one mentioned being thirty feet long and six feet thick. As 
in ordinary rock-boulders, the angles of the sand-boulders are rounded 
as if by attrition. They lie in fine clay containing but little sand, and 
are sharply defined from the surrounding matrix. Planes of stratifica- 
tion show that the masses of sand were derived from some sub-aqueous 
deposit; and the stratification of the clay in which they are imbedded, 
leads the author to conclude that it too is subaqvieous. Professor Spen- 
cer suggests that " these deposits were probably made in a shallow arm 
of the sea, cut off by the Ozark ridge rising a few hundred feet higher; 
yet the waters may have been either brackish or even fresher — as the 
gulf of Obi today, owing to the amount of fresh water pouring into it; 
and not to a glacial lake." 
We are to conceive of a condition of things in central Missouri similar 
to what now obtains along sandy shores, particularly in shallow bays 
north of the arctic circle. During the cold winters floe-ice formed 
around the margins of this "arm of the sea," and into the lower surface 
of the floe, the stratified sand was frozen to a depth of several feet. In 
the spring the sand and ice, incorporated into one mass by the agency of 
frost, was broken up and floated away ; the frozen sand, losing its angles 
and overcoming the buoyancy of the ice, as the latter was diminished 
