62 F. T. THWAITES 
The absence of similar deposits of proved Ordovician age, 
together with the lack of induration and the presence of the gravel- 
filled gashes in the sandstone, definitely eliminate the first 
hypothesis. 
The second theory may be divided into three subdivisions: 
(a) distant source for the dolomite slab; (6) movement by rotation 
without transportation to any great distance; (c) slight lateral 
movement causing the opening of an irregular bedding plane by 
destroying the registry of the irregularities. 
a) No nearby source for such a gigantic slab (at least two 
hundred feet square) can be found except on the hill northwest of 
the quarry, and a glacial movement from the northwest is impossible 
since the Driftless Area is not very far away in that direction. The 
glacial transportation without breaking of such an enormous 
piece of rock for any distance, as from across the valley to the 
east, is quite out of the question. The rock above the gravel seam 
is no more broken than is usual near the surface of the ground. 
The major joints, which strike from N. 5° W. to N. 30° W. pass 
right through the gravel seam (Figs. 5 and 6) and there seems no 
valid reason to assign a glacial or post-glacial age to them. In 
fact, there is no difference in the rocks above from those below the 
seam and no glacial striations are found on the under surface. 
b) The second subdivision, namely, the inclusion of gravels by a 
rotary movement of the overlying rocks, is open to the same 
objections. It also necessarily involves the assumption of the 
glacial origin of the fold. 
c) The opening of an irregular bedding plane by a slight move- 
ment, either rotary or lateral, which destroyed the registry of the 
irregularities is a possibility. ‘The seam is, however, very regular; 
moreover, the glacial or post-glacial origin of the joints must be 
presupposed under this hypothesis. 
The third view, the raising of the overlying beds by glacial 
action thus opening a seam, as one opens the leaves of a book, 
offers the fewest difficulties. However, it seems impossible that 
such a process could avoid moving and breaking the overlying rocks. 
A further difficulty is the comparatively regular thickness of fine 
gravel. If the frozen upper layers were simply buckled upward 
