Proceedings. 313 



Range 21, the rock being generally of a brownish-black shade, although 

 the paste-rock being rather ferruginous, weathers through alteration to a 

 considerable friability with the production of much coloring matter. It is 

 conspicuous that the pebbles held conglomeratically by this rock-paste are 

 often large — i. e., 6 to 10 inches in diameter, quite generally well rounded, 

 and of a nearly uniform lithological structure and constitution. Jn 

 composition they may be roughly described as a fine-grained trap. 



The amygdaloidal rocks are to be seen both above and below the con- 

 glomerate exposures, beginning at Chengwatona dam and continuing to 

 the banks of the St. Croix river. The color and hardness vary consider- 

 ably ; the dark purple varieties are usually softer than the brick reds. In- 

 clusions are as a rule crystalline — the cavity diameter ranging from 1-16 to 

 ^ in., and the mineral closely resembling Thomsonite. 



In the epidotic material of the veins in the rocks mentioned above, na- 

 tive copper is sparingly found. And at the location of the "Chengwatona 

 copper mine," where considerable boring and some shafting have been 

 done, the writer obtained a crystal of native copper and silver alloy. This 

 metallic crystal is about 3^ in. in diameter, rising from the vein rock in a 

 single termination. A portion of its mass examined qualitatively in the 

 wet way, demonstrated the presence of both silver and copper, but no 

 quantitative analyses have been effected. 



The members of this Academy will call to mind that northward from 

 this region 12 to 15 miles are the Hinckley sandstones, now much quarried 

 for building material. That also within a few miles are outcroppings of 

 trap rock. These conglomerates and amygdaloids rise at irregular inter- 

 vals above the horizon, the rounded masses frequently similar in mere out- 

 ward appearance to the granitic masses in Stearns Co. Inasmuch as no 

 contact points between these Snake river rocks and the sandstones and 

 traps mentioned above, have come under the author's observation, he does 

 not venture an opinion as to their geological relationship. This last point, 

 together with conclusions as to range direction, through this comparatively 

 level, sometimes low and swampy region ; as well as to results respecting 

 the micro-lithological structure of these rocks and their accompanying 

 minerals, form the subject for his further attention. 



The development of Acrostalgnins conidia bearers, by 

 Professor Conway MacMillan. 



List of European plants introduced into the valley of the 

 Minnesota river, by Professor MacMillan (read by title). 



An Epinastic Potato plant, by Professor MacMillan. 



The following gifts to the museum were received from S. C. 

 Gale, Esq. : one alligator, a stuffed specimen ; one Tctrodon 

 turgidiis mitch; one Diadon hystrix L., from Florida, for which 

 the secretary was instructed to express the grateful acknowledg- 

 ments of the Academy. 



Professor Nachtrieb gave a brief and infomial account of 

 the summer's work of the zoological survc}' of Minnesota. 



