After determining, by the more minute and detailed exam- 

 inations, the stratified nature of these rocks, we are able to 

 discover in the larger masses, and the hill escarpments the 

 direction and dip of the strata, which are extremely obscure, 

 and rendered more difficult of observation by the numerous 

 joints. Besides these determinations, I have in two or three 

 localities been able to trace these quartzites upward till the 

 beds become conglomeritic ; the pebbles consisting of the 

 crystalline quartz, (usually of a brown color,) which vary from 

 the size of peas to a foot or more in diameter. The darker 

 materials gradually become mixed with a lighter colored sand, 

 and sometimes a notable proportion of argillaceous matter ; 

 the mass loses its metamorphic aspect, and we find ourselves 

 almost imperceptibly investigating the base of the Potsdam 

 sandstone. 



It must not be understood, however, that there is any pass- 

 age from the one to the other that would indicate a synchron- 

 ism of the two formations. On the other hand, the quartzite 

 had been deposited as a coarse and find sand, (with sometimes 

 pebbles, had become metamorphosed and the mass raised in 

 low axes before the commencement of the Potsdam era. The 

 breaking up of this mass gave the pebbles of quartz, etc., 

 which lie at the base of the Potsdam sandstone ; and these 

 pebbles,) with an accumulation of sand from the breaking up 

 of the mass continue the color and aspect of the rock below, 

 till the influx of lighter colored sand changes the character 

 and color of the whole. 



I regard this discovery of the nature of these underlying 

 masses to be a matter of considerable interest ; and since the 

 areas occupied by such rocks are limited, and it is nearly im- 

 possible to trace a connection between any two of them, it 

 becomes important to collect material from numerous localities, 

 for the purpose of comparison with the more extended areas 

 of older metamorphic rocks. 



These metamorphic masses are, in all probability, extensions 

 of the Huronian formations of Canada ; and though not fa- 

 miliar with the latter in its typical localities, I am inclined to 

 refer them to that period, since they do not correspond with 

 the Laurentian rocks known to me through investigations in 

 northern New York. 



I have considered these facts of sufficient interest to the 

 science of Geology and to the survey to communicate them in 

 the present report. I shall continue this investigation, and 

 hope to be able hereafter [to show the relations of all these 

 metamorphic masses to formations of known geological age. 



