THE 
AMERICAN GEOLOGIST 
Vol. XVII. JUNE, 1896. No. 6. 
LOG-LIKE CONCRETIONS AND FOSSIL SHORES. 
By J. E. Todd, Vermillion, S. D. 
(Plate XII.) 
During the past season it was my privilege to visit the Lar- 
amie formation of western Dakota about the head waters of 
the Grand and Moreau rivers. The formation is composed of 
alternations of sand, often passing into yellow loam resem- 
bling loess, with drab-colored clays and beds of lignite. The 
sands are in places hardened into massive sandstone, but are 
more frequently incoherent. My attention was called, in my 
earlier acquaintance with the formation, to peculiar elongated 
concretions lying in the beds of sand. These were particu- 
larly conspicuous about prominent points of the landscape. 
One of the first views observed is shown in plate XII, figure 1. 
It represents a series of these concretions extending a distance 
of 100 feet and lying in strict order end to end. On either 
side others are seen less regularly arranged with their axes 
approximately parallel. Closer examination revealed the fact 
that they are composed of fine sand cemented together with 
calcareous matter and showing wavy lamination or ripple 
marks. The separate blocks or segments are separated by 
square joints, except at the ends of the series, where they are 
rounded. One block at the locality especially attracted my 
attention. It was about twelve feet in length and two feet in 
diameter. When viewed from one side it had the exact ap- 
