340 PLEISTOCENE OF INDIANA AND MICHIGAN. 



water offshore. Where the water is shallow for a long distance out, storm waves break at a 

 considerable distance off shore and do a great work of erosion upon the bottom. They pound 

 it and stir it up, ultimately carrying away the finer sediments to deeper water and sweeping 

 the coarser sediments up the slope into a beach ridge. Thus, in front of a beach ridge of fairly 

 mature development, there is commonly a belt of considerable width — a "surf-wasted zone" — 

 which has been cut away by the subaqueous work of waves and currents. None of the spur 

 ridges of this district has a surf-wasted zone. In strong contrast, the middle beach of Lake 

 Maumee, a mile or so away, has a well-developed zone of this kind. 



When to the several peculiarities adduced is added the clayey composition of the ridges, it 

 becomes impossible to explain them as normal, unmodified products of wave and shore current 

 action. But, as will be pointed out below, all of their peculiarities are clearly explained if the 

 ridges are regarded as ice ramparts. 



East of Pandora the rampart ridges have somewhat different expression. They are more 

 nearly straight but vary more in strength and height and are more largely composed of clay. 

 Some of their higher parts reach an altitude of 800 feet. The highest beach of Lake Maumee 

 has an altitude of 785 to 790 feet, and the ridges east of Pandora seem quite clearly to belong to 

 the time of that beach, as do also some smaller, scattered fragments 3 miles south of Pandora 

 and 3 to 4 miles southeast and south of Columbus Grove. 



From Pandora to Benton Ridge the middle Maumee beach seems to rise 15 feet and runs 

 obliquely across the trend of the rampart ridges. It has the appearance of having been super- 

 posed upon the rampart ridges, and there is reason to believe that the ramparts formerly ex- 

 tended farther to the northeast on ground which is now below the level of the middle beach. 



FORMATION. 



In its early stages Lake Maumee was hi all probability covered with ice of considerable 

 thickness during whiter seasons. In the spring the margin of the ice, where it had been attached 

 to the shore, was the first to thaw, leaving a lane of open water between it and the land. The 

 ice had thus become loosened from the land and floated freely on the water. While hi this 

 condition, strong winds from the west or northwest drove it toward the east or southeast, and 

 the force of the wind and the momentum thus attained carried it up the gentle slope. 



In this district the shore and lake bottom conditions at the time of the highest beach of Lake 

 Maumee were extremely favorable for the formation of ice ramparts. When the vast ice cake 

 or floe impelled by the wind began to move toward the shore its lower edge first encountered 

 the gently sloping clayey bottom of the offshore shallows. This offered relatively little re- 

 sistance. A considerable body of the mud with whatever was resting on it was pushed forward 

 at the edge of the ice. At length the upward inclination of the bottom raised the marginal part 

 of the ice slightly out of its horizontal position and made it conform to the plane of the slope. 

 Probabhy the ice was cracked at intervals in this process, but it was not broken up and displaced. 

 When the edge of the ice reached the beach line, the materials which the waves had gathered 

 were incorporated with the mud and pushed along up the slope. When the shoreward move- 

 ment of the ice stopped, this body of clay, gravel, and sand was left as the rampart ridge. The 

 bent ends were pushed back at the edge of ice moving from a northwesterly direction, and the 

 crooks and thickened ends were produced and the clay contributed in the same way. Such a 

 process requires no notable depression hi the gap west of the bent ends nor any surf-wasted zone 

 in front of the spurs. 



In all probability the ice cakes involved were generally several miles in extent along the 

 shore. This is indicated by the length of the rampart spurs. That the ice cakes were not 

 much broken along then shoreward edges is also indicated by the straightness of most of the 

 longer spurs. Still the occasional sharp bends and the bent ends may be in part due to cracking 

 of the ice on lines normal to the shore and to unequal shoving of the different parts. Whether 

 the ramparts are in each case the product of a single onshore movement or are the cumulative 

 product of a few or of many such movements can not now be stated. The latter alternative 

 would seem the more likely one, but very little evidence supporting it was observed. 



