CONTRIBUTIONS TO l»AL-ffiONTOLOGT. 219 



rizontal, and not penetrated by trap dykes, wliich sometimes cut 

 the rock immediately beneath. The present aspect of the forma- 

 tions indicates a greater easterly extension of the upper sandstone 

 than of the lower formation ; while in a westerly direction, we 

 know little of the higher sandstone beyond the eastern portions 

 of Minnesota*. 



Whether we may have, in the Lake Superior region, evidences of 

 more than two periods in the accumulation of the conglomerates 

 shales and sandstones, indicated by want of conformity one with 

 the other, I am not prepared to assert from my own observations. 

 I have already cited the opinion of Dr. Houghton regarding the 

 sandstone in its eastern extension towards the outlet of the lake, 

 together with corroborative evidence from other sources, that this 

 sandstone is of the age of the Chazy formation. In a later Report 

 (1841), Dr. Houghton recognizes a quadruple division of the sedi- 

 mentary formations in the following order : 1st, "Conglomerate 

 rock;" 2d, " Mixed conglomerate and sandrock ;" 3d, '* Red sand- 

 stone and shales ;" and 4th, " Upper or Gray sandrock." Of the 

 third division, he remarks, p. 40 : " The red sandrock is less fre- 

 " quently traversed by dykes of trap than either of the rocks 

 " before described, though dykes were several times noticed tra- 

 *' versing the whole of the several formations up to and including 

 " the Red sandstone." Of the fourth division, he says ( p. 52) : 

 "The composition of this rock differs from that of the lower 

 *' sandrock, in being more exclusively quartzy, while in epoch of 

 " deposition, the rock under consideration should not be con- 

 *' founded with that of the Red sandstone, it has already been 

 " stated that the Red sandstone of the south coast dips regularly 

 " northerly, while the upper or Gray sandstone dips equally re- 

 " gularly south or southeasterly ; in which respect the last men- 

 ** tioned rock conforms to the limestone resting upon it, while it 

 " rests itself upon the uptilted edge of the red sandrock below." 



We have therefore an unequivocal assertion of the unconform- 

 ability of the upper sandstone with the rocks belowf. 



* We know, however, from the explorations of Dr. Hayden. of the occirrence of 

 the older sandstone towards the base of the Rocky mountains (judging from the fos- 

 sils), and we suppose that this may be connected with that of the Mississippi valley, 

 and may have had a similar source. It is known that rocks of Huronian age extend 

 westerly and northwesterly from the south side of Lake Superior, and these at ono 

 time may have furnished the materials for the deposits. Still, this would not make an 

 object ion, but rather sustain the argument I have advanced, so far as I have know- 

 ledge of the occurrence of this rock. 



t It would appear, however, that at a subsequent period. Dr. Houghton was in- 

 duced to regard the conglomerates and red sandstones and shales which are penetrated 

 by trap rocks, to be of the New Red sandstone. 



