IV APPENDIX. 



"Were the waters of the Gulf of California suddenly changed 

 to gravel and sand, with its precipitous and rugged mountain 

 islands left projecting from the surface as now, there would be 

 so [produced an excellent representation of these deserts, and, 

 geologically speaking, it is but as yesterday that precisely the 

 same action was going on over all this enormous area as is now 

 in progress in the more confined region of the Gulf The slow 

 elevation which has in part probably caused the gradual receding 

 of the waters, may still be extending the area of our continent." 



Up to this time Mr. Marvine's geological studies had been 

 somewhat general and desultory — necessarily so from the condi- 

 tions under which they were made. But in the following summer 

 he was engaged with Professor Pumpelly in the Keweenaw Cop- 

 per Region on the shore of Lake Superior, and his report on this 

 work was published by authority of the Legislature of Michigan. 



His work during this season was confined to a narrow area, 

 and was special, and is a fine example of painstaking, minute 

 geological study. It consisted in tracing a series of geological 

 beds through two or three counties lying along the lake shore. 

 This was done by careful triangulation and levelling of the gene- 

 ral area, and the following of the dips and strikes of the beds 

 and measuring their thicknesses, and by carefully analyzing their 

 lithologic and mineralogic constituents. The entire work is pre- 

 sented in a series of sections and tables carefully and skilfully 

 arranged, with a general discussion, sufficiently elaborate to set 

 forth the relations of all the important facts. His work is thus 

 a fine model for what must be done throughout the Lake Superior 

 region before any general discussion of the geology of the district 

 can be made which will have permanent value. 



Mr. Marvine thus demonstrated that his experience in the 

 fragmentary work incident to a geological reconnoissance had 

 not led to such habits of hasty conclusion as to incapacitate him 

 for the more thorough work of a geological survey. 



Yet up to this time his work was but fragmentary, but in 

 March, 1813, he was given a position as geologist in the corps 

 of the IJ. S. Geological and Geographical Survey of the Terri- 

 tories under Dr. Hayden. 



During the following season his field of research embraced the 

 region of Middle Park in Colorado Territory, including the 

 mountains by which it is inclosed, and extending eastward to 

 the Great Plains, embracing an area of about 5000 square miles. 

 How thoroughly his work was done, how clearly the geography 

 and geology of the region was set forth in his report, and what 

 important conclusions he reached in mountain structure and geo- 

 logical history, can only be fully appreciated by a careful and 

 thorough reading of his report. It is impossible to undei'stand 

 a discussion of the geological structure of a region without first 

 fully grasping the character and magnitude of its geographic 



(56) 



