304 Geology of the Lakes and the Valley of the Mississippi. 



in other respects, being that the limestone has changed place with 

 the alum slate or lias clay which here rests immediately on the red 

 marie of the sandstone. The shale is bituminous, and might possi- 

 bly support a low degree of combustion. Its thickness is about 

 thirty yards. Doctor Mitchell confounded it with the transition and 

 primhive slates, fancying that he had traced it from beneath the 

 granite of the Hudson through various windings to the foot of the 

 cataract. 



The coast of lake Erie, though really a dangerous one, is any 

 thing in appearance but iron-bound. Down to the water's edge it 

 is earthy, and without rocks, except at Point Albino on the British 

 side ; and the limestone, though forming the entire basin, rises above 

 the surface of the water, for the first time, at the Bay of Sandusky, 

 in a coarse granular form, imbedding numberless ammonites, ortho- 

 ceratites, terebratulse, and other shells. Is not this the muschelkalk 

 or its equivalent ? The shells are so thickly disseminated in it, that 

 it is rare to find a piece of it as large as a cabinet specimen, without 

 one or more of them. It is easily got out in blocks, works well, and 

 at Detroit, is advantageously \ised as a building stone. Its place in 

 the group is perhaps inferior to the compact limestone of the islands, 

 remarkable for the profusion of its sulphate of strontian contained in 

 druses. This drusy limestone is perhaps the uppermost rock in the 

 valley of the Mississippi, for there is no trace of oohte, chalk, or any 

 thing as recent. The extent of the formation westward is indefi- 

 nite ; but it probably reaches to the Missouri, which passes from the 

 mouth of the Platte to the Mississippi, through extensive fields of 

 horizontal and tabular limestone. 



The retrocession of the cataract from Queenstown Heights, and 

 the time supposed to have elapsed in accomplishing the present dis- 

 tance, are subjects of curious but unprofitable speculation, whose re- 

 sults must disappoint the expectation of those who think, by means 

 of a comparison of the rate with the distance, to fix the date of the 

 commencement of it. Professor Rogers ingeniously maintains in 

 the late January number of this Journal, that the cataract had not 

 its commencement at Queenstown Heights at all. The spectator 

 who forms his judgment on the intrinsic evidence of the scene, will 

 probably concur in the opinion generally received, that it in fact be- 

 gan at that place ; but he will be satisfied that it aflbrds no data to 

 compute the duration of the recession with any thing like an ap- 

 proach to the truth. When we see the riv^er working in the rock 



