Fink: ROCK LICIIKNS 01 TAVI.OKS FALLS. 3 



so closely in the last two localities for lichens not^strictly char- 

 acteristic of rocks, but still growing on them occasionally, 

 about offsets the limited time spent in examining the area form- 

 ing the basis of the thoughts here presented, so that the numbers 

 given above, save for difference in areas covered in the three 

 instances, may still be taken to represent, approximately, rela- 

 tive richness in rock lichens. But again, the Taylors Falls 

 area, with one possible exception, gave me more such lichens 

 collected in the two days than are recorded in any State list 

 hitherto published. 



The igneous rocks at Taylors Falls are essentially like those 

 which outcrop occasionally between this place and Lake Su- 

 perior, and the fact that Taylors Falls is practically the south- 

 ern limit of outcrop of these rocks furnished the first suggestion 

 of the interest involved in an analysis of their lichen-flora. 

 Of the 79 species and varieties collected, only 8 are plants not 

 yet found further south in Minnesota or Iowa. These 8 I have 

 also found along Lake Superior, and they are species not com- 

 monly occurring further south except at high elevations. These 

 are Biatora rufonigra Tuck., Lecidea alboccertilescens Schasr., 

 three forms of Bucllia petraa (Flot., Koerb.) Tuck., Umbili- 

 caria dillenii Tuck., Nephroma helveticum Ach. and Ephebc 

 solida Born., all forms found on the igneous rocks and none of 

 them on the sandstone. Subtracting the 8 species and varieties 

 leaves 58 rock lichens, nearly all of which occur in other por- 

 tions of the southern half of Minnesota, but not all on rocks. 

 Those not known to flourish on rocks in other parts of the State 

 grow on them here under unusually favorable conditions to be 

 explained below. 



What has already been stated, especially the last paragraph 

 above, merely suggests the problems of interest which I shall 

 attempt to discuss and which involve a knowledge of geological 

 conditions present and past, as well as acquaintance with lichen- 

 species and their distribution in general. For the geological 

 data concerning this area, I have relied largely on the researches 

 of Dr. Charles P. Berkey, who has recently studied the region 

 including Taylors Falls in detail, and who is therefore especially 

 able to give the information needed for my purpose. The ques- 

 tions which I shall consider below are those which thrust them- 

 selves upon me as I observed and studied this extremely in- 

 teresting lichen-flora ; and though the area is a small one, the 



