Cojtper Mining in Minnrsafa ILtll. 107 



the Sfc. Cvoix at the head o£ the Dalles, this rock is quite ]H)ri)hyn- 

 tic; elsewhere it is (juite ain3g<laloidal: the aiiiygdaloidal structure 

 i^ the more prevalent, and at the surface the rock usually is much 

 decomposed. At Daluth the huge masses of rock which Strerig 

 and K loos first called hornblende gabbro comes in, ver^' coarse grained 

 and massive. Further down the lake, gabbro, diabases, both 

 •massive and of the ash bed type, felsite porphyries and quartz por- 

 phyries occur.* 



MtN'iNG FOR Coi'i»ER.^ — Copper mining has never been pros- 

 ^secuted on a large scale in this state. The presence of the copper 

 bearing rocks lias led to a great deal of conjecture and to no incon- 

 siderable amount of exploration: the frequent discovei-y of pieces 

 of float copper, i.e. of pieces in the material of the glacial drift, 

 completely isolated from all rock and mineral material which 

 would indicate the presence of that metal, has also led to the care- 

 ful examination of many localities which otherwise would never 

 have been thought of as mining districts. I believe LeSneur was 

 the first pne to h'nd one of these masses. His find was, according 

 to Dr. Neill^ near a small lake in the Mississippi valley, four 

 leagues above the mouth of the river St. Croix. Among the num- 

 berless pieces which have since been found, the Academy owns 

 •one of the largest:— a mass of 75 lbs. weight found three or four 

 years ago at Taylors Falls and ])resented "to" the Academy by Mr. 

 Oeo. H. Miller. 



The first mining operations were also undertaken by Le 

 Sueur. Copper had been found at some point now unknown in 

 the valley of th-^ Blu^ L] irth river and had bien assayed in Paris 

 in 169G. LeSueur wintering in 1700-1701 near the junction of the 

 Blue Earth and St. Peter rivers, as the spring opened worked out 

 an enormous quantity of ore. and selecting 4,000 lbs. started with 

 it down the St. l*eter and the Mississippi in order to ship his treas- 

 ^ire to France. Since that time a great many explorers have looked 

 for the immense deposits said to have been found by LeSueur, 



*A very interesting summary of the Minnesota Keweenaw rocks appears 

 ill a paper by Professor Irving, published as an "accompanying paper" in the 

 Third Annual Report of the Director U. S. Geol. Survey, pp. 89-188 incl. 

 Many of the facts here given are abstracted from that report recently |)ub 

 lished. 



