190 



Contributions to Palceontology. 



times cut the rock immediately beneath. The present 

 aspect of the formations indicates a greater easterly exten- 

 sion 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. 1 



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 toward 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 sedimentary formations in the following 

 order: 1st, "Conglomerate rock;" 2d, " Mixed conglo- 

 merate and sandrock;" 3d, "Red sandstone and shales;" 

 and 4th, "Upper or Gray sandrock." Of the third divi- 

 sion, 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 traversing 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 confounded with 



1 We know, however, from the explorations of Dr. Hayden, of the occur- 

 rence of the older sandstone towards the base of the Rocky Mountains 

 (judging from the fossils) ; 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 one time must have 

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

 objection, but rather sustain the argument I have advanced, so far as I 

 have knowledge of the occurence of this rock. 



