ANALYTICAL ABSTRACTS. 309 



Minnesota as resting unconformably upon a pre- Paleozoic floor. The base of 

 the Potsdam is usually conglomeratic. At Minneopa a well 800 feet deep 

 passed through a conglomerate for a distance of 225 feet, the pebbles of 

 which are vitreous quartzite like those occurring in Cortland, Watonwan and 

 Cottonwood counties. A conglomerate coiitaining granitic debris is found on 

 Snake river about two miles above Mora, and three miles distant from the 

 Ann River knobs of hornblende -biotite- granite, the clastic appearing to be 

 derived from the granite. At Taylors' Falls a conglomerate made up of 

 pebbles of diabase rests upon the diabase of the St. Croix river. These 

 underlying formations are Archean and Algonkian rocks. 



Grant ' states that the Animikie rests unconformably upon the Saganaga 

 granite ; that the Ogishki conglomerate is intruded by the Saganaga granite, 

 and therefore that the Ogishki conglomerate is earlier than and separated by 

 a great structural break from the Saganaga granite. As the Keewatin has 

 the same relations to the Saganaga granite as the Ogishki conglomerate, the 

 same thing is true of the Animikie and Keewatin. The Ogishki conglomerate 

 is younger than the most of the Keewatin, but is considered as a part of it. 



Comments : — The most characteristic and abundant fragments in the 

 Ogishki conglomerate are granite. The rock occurs in pieces running from 

 those of minute size to great bowlders. It is manifest that this material was 

 derived from a pre-existing granite. These bowlders are in all respects like 

 much of the Saganaga granite, and the probability is very strong that this is 

 their source. Grant is probably correct as to the intrusion of the conglomerate 

 by a granite, but this granite may have also intruded the main Saganaga 

 mass. The too frequent mistake has apparently been made of concluding 

 that in the Saganaga area there is granite of but one age, when frequently in 

 the great massives of the Northwest, granites of several ages occur, the 

 latest ones cutting all the previous ones, and often the far newer elastics. 

 It further follows that the implication that the Animikie is unconformably 

 upon the Ogishki conglomerate needs the support of additional evidence. 

 That this conglomerate is possibly more nearly related to the Animikie than 

 to the Keewatin is shown by the presence of abundant jasper fragments, pre- 

 sumably derived from the Keewatin. The article appears to be another 

 illustration of the facts being right, the author in his interpretation, however, 

 overlooking a part of the facts which are to be accounted for in making a 

 true generalization. 



Winchell ^ gives a review of the literature on the Norian of the Northwest. 

 Here are included the gabbros, placed as the basement member of the 



' The Stratigraphic Position of the Ogishke Conglomerate of Northeastern Min7tesota. 

 U. S. Grant. Am. Geologist, vol. 10, 1892, pp. 4-10. 



= The Norian of the Northwest, by N. H. Winchell. In Bull. 8, Geol. and Nat. Hist. 

 Sur., Minn. 1893, pp. iii-xxii. 



