176 BULLETIN 109, UNITED STATES NATIONAL MUSEUM. 



which Doctor Houghton's personal contribution is 89 pages. This is 

 by far the most important report of the entire series, both for what 

 Doctor Houghton presents, and for what is contributed by his two 

 geological assistants, Douglass and Hubbard. 



Doctor Houghton's report is dated February 1, 1841, and his 

 personal statements are devoted to the " northern slope of the Upper 

 Peninsula." Ten pages are occupied with "General description and 

 topographical features." He complains bitterly of the misleading 

 character of the maps of the American border of Lake Superior. 



Scarcely a single feature of tlie interior is given as actually exists.' * « * 

 Tlie coast lines are so defective as scarcely to be recognized, except in their 

 most general outlines. 



A comprehensive description of the great physiographic features 

 of the whole Upper Peninsula is followed by a particular enumera- 

 tion of the principal streams. A general sketch of He Royalo 

 follows, with a notice of the region west of Pigeon Eiver, on the 

 north shore of Lake Superior as far as the Lake of the Woods, the 

 hilly portion of which, " though of exceeding interest in a geo- 

 logical point of view, is the most desolate that could be conceived " 

 (p. 13). 



Under the " General geology of the Upper Peninsula," the follow- 

 ing groupings are observed : 



1. Primary rochs. — These consist chiefly of granite, syenite, and 

 syenitic granite. First seen on the coast at Little Presque Isle, they 

 reappear frequently nearly as far as Huron Eiver and islands, and 

 are thence confined to a range of hills back frcm the coast, rising 300 

 to 700 feet above the lake, and continuing m a southwesterly direc- 

 tion. A portion of the southwesterly prolongation of the Porcupine 

 Mountain range is made up of rocks belonging to this group. 



But little typical granite is found. 



The more common rock is made up of quartz, feldspar, and hornblende, 

 giving rise to a very dark colored syenite. Occasionally mica enters sufficiently 

 into the compound to form syenitic gianite. (P. 23.) 



The southeasterly portion of the range is most quartzose. As we 

 proceed norwesterly the rocks approach a quartzless " compound of 

 feldspar and hornblende, which then assumes a granular structure, 

 constituting greenstone." The intermediate rock " may not in- 

 appropriately be called a syenitic greenstone." 



The primary rocks between Little Presque Isle and Huron River 

 are mostly compact and fine-grained syenite or syenitic granite. In 

 their southwesterly continuation they are largely traversed by dikes 

 " similar in composition to the greenstone before mentioned. These 

 have produced rnetamorphic changes in the contiguous rocks, extend- 

 ing to several hundred feet." These dikes are regarded as existing 



