BIG COTTONWOOD FORMATION 231 



right angles to that of the Courtland quartzite at Eedstone, but conforms 

 in direction with that of the Cambrian and Ordovician beyond the Eed- 

 stone quartzite mass. The hatter is in seaward direction from the New 

 Ulm basal conglomerate, and its present elevation and position are such 

 as to indicate that in the Cambrian sea it must have stood as a high island 

 or peninsula, and that the New Ulm conglomerate is or was continuous 

 with the Cambrian basal conglomerate east of Eedstone as at ]\Iinneopa 

 falls. 



At Minneopa falls, near Mankato, on the south side of the Minnesota 

 Eiver valley, a well was bored 1,000 feet deep. 



"In boring, 575 feet fi'om the surface a conglomerate was reached with peb- 

 bles of clear, fine, non-granular quartzite up to 2 or more inches in diameter. 

 From this depth to more than 800 feet below the surface the borings consisted 

 chiefly of quartzite pebbles indistinguishable in macroscopic and microscopic 

 characters from the vitrified quartzite at Courtland. These pebbles are essen- 

 tially different from those composing the 'basal conglomerate' beds opposite 

 New Ulm" (Hall, 10, pages 23-24). 



I have examined, with Professor Hall's permission, pebbles from the 

 Minneopa well and find that they have surface pitting and general charac- 

 teristic form of the quartzite pebbles from the New Ulm conglomerate. 

 If both are, as they now appear to be, parts of the same Cambrian basal 

 conglomerate, then the difference in the prevailing rock constituent of the 

 pebbles is a local one, indicating that the rock t3'pes, as seen in the outcrop 

 of the New Ulm conglomerate quartzite, are of local derivation. 



The geologic formations which appear in the ]\Iinneopa well are trace- 

 able toward New Ulm. The Jordan sandstone disappears from over the 

 Saint Lawrence shales before reaching Judson, at which place the latter 

 outcrops for 1 or 2 miles. Beyond Judson a lower siindstone rises into 

 view along the railway, but is not seen beyond Camljria. The Cretaceous 

 shales appear l^etweon Cambria and New Ulm, showing that the Cambrian 

 had been deeply eroded on the south of the Eedstone after Camljrian time, 

 since the Cretaceous lies doubtlessly in unconforniit}' in its place. 



The Big Cottonwood FoiiiiATioN: Cretaceous 



Shales and sandstones of Cretaceous age have been heretofore recog- 

 nized in isolated outcroppings on the Big Cottonwood river and in neigh- 

 boring parts of the Minnesota valley. Fossil leaves from certain sand- 

 stone strata have been described by Lesquereux (4 and 5), and from evi- 

 dence afforded by these fossil plants he referred the formation to the 

 Dakota group. Certain green shales which Avere supposed to lie higher 

 than the fossiliferous sandstone, have been referred to the Niobrara group 

 by Winchell and Upham {6, volume 1, page 576; volume 2, page 165). 



