Age of the Missouri ]^iz'cr. — L'phaiii. 87 
off in gentle slopes, but far more often rose as sheer cliffs, with narr(ju 
ledges along their fronts. A sparse growth of grass covered certain 
portions of these lands, and on some of the steep hillsides, or in the can- 
yons, were scanty groves of coniferous evergreens, so stunted by the 
thin soil and bleak weather that many of them were bushes rather than 
trees. Most of the peaks and ridges, and many of the valleys, were 
entirely bare of vegetation, and these had been cut by wind and water 
into the strangest and most fantastic shapes. Indeed it is difficult, in 
looking at such formations, to get rid of the feeling that their curiously 
twisted and contorted forms are due to some vast volcanic upheavals or 
other subterranean forces ; yet they are merely caused by the action 
of the various weathering forces of the dry climnte on tl'.e different strata 
of sandstones, clays, and marls. Isolated columns shoot up into the 
air, bearing on their summits flat rocks like tables ; square buttes tower 
high above surrounding depressions which are so cut up by twisting gul- 
lies and low ridges as to be almost impassable ; shelving masses of sand- 
stone jut out over the sides of the cliffs ; some of the ridges, with per- 
fectly perpendicular sides, are so worn away that they stand up like 
gigantic knife blades ; and gulches, wash-outs, and canyons dig out the 
sides of each butte, while between them are thrust out long spurs, with 
sharp ragged tops. 
VARIATION IN THICKNESS OF THE SUBDIVI- 
SIONS OF THE ORDOVICIAN OF INDIANA. 
With notes on the range of certain fossils. 
By Aug. F. Foekste, Dayton, O. 
PLATE V. 
CONTKNTS. 
I. Variations in Thickness of Ordovician Strata in Indiana. 
1. The Subdivisions of the Ordovician of Ohio and Indiana 88 
•S. Diminution in Thiclvness of Ftica. Lorraine, and Ulchmond south- 
ward 88 
3. Diminution in Thicltness of the Subdivisions of the Lorraine. ... 89 
4. Diminution in Thiclvness of the Subdivisions of the Richmond.. 91 
a. Intervals between IlerbertoUa iusculpta layer, the base of 
the AVaynesville and ton of the Whitewater beds north of 
Madison 91 
b. Thickness of Hebertella Inscnlpta layer 93 
. c. Interval between Ilerberrella insculpta layer and base of Di- 
northis subquadrata zone 93 
d. The Vertical range of Dinorthis subquadrata north of Madison. 93 
e. The Vertical range of Dinorthis subquadrata south of Madison. 94 
f. The Dalmanella jugosa zone of the AVaynesville bed 95 
g. The Madison bed 93 
II. The Vertical Itange of Ortaln Ordovician Brachiopoda . 
5. Dalmanella emacerata. D. nuiltisecta. D. meeki. !>. jugosa 96 
C. Strophomena hallie, Str. planiconvexa. Str. plancinbona. Str. ne- 
gl^cta, Str. vetusta, Str. nutans, Str. sulcata 9s 
