Relation of the Sandstone^ etc.^ of the Baraboo Valley. 125 



joints in the same manner as the cliffs at Devil's lake. At the 

 extreme southern end, the rock varies from a compact, dark- 

 colored, homogenous quartzite to a much less compact and 

 lighter quartzite. One large detached block of the hard, dark 

 quartzite was seen beautifully covered with ripple-marks. 

 Passing along the face of the cliff toward the north, it becomes 

 covered with large blocks of quartzite, sandstone and con- 

 glomerate, which have fallen from above. Coming to the ex- 

 posed rock again, it changes to a metamorphic conglomerate. 

 This makes up more than half the section. It consists of an- 

 gular pieces of the compact, dark quartzite, firmly imbedded 

 in a cement of white crystalline quartz. The former vary in 

 size from small fragments to masses several tons in weight. 

 Numerous cavities are lined with quartz crystals. The dip 

 here is from 75-80 <=> N. 



Fig. 2. 



3 3 1 2^ 1 



1, Quartzite. 2, Metamorpliic Conglomerate. 3, Potsdam Sandstone. 4, 5, Conglom- 

 erates. 6, Drift. 



The remainder of the section consists of the homogeneous, 

 dark, compact quartzite, bedded in the same manner. We 

 have indications then of these successive sets of circumstances 

 in Azoic times ; those in which were formed respectively the 

 underlying quartzite, the conglomerate and the overlying 

 quartzite. The lower quartzite must have been already hard- 

 ened from the moving sands before it was broken into frag- 

 ments for its conglomerate. And then its cement was crystal- 

 lized. Finally layers of sand spread over this were hardened. 

 As has been said, upon the southern flank of this Azoic core, 

 horizontal beds of Potsdam sandstone lie unconformably. They 

 extend a short distance over the edges of the upturned beds 

 of quartzite. The relations of this sandstone to the underly- 



