122 A. WINCH ELL A LAST WORD WITH THE HURONIAN. 



which have been rolled on the shore of a gentle sea, with frequent intervals 

 of calm, accompanied by aluminous deposition. Limestone from the east 

 side of Echo lake (XXVI, 13) presents almost exactly the same appear- 

 ances, with a slightly larger volume of decomposition products giving denser 

 lines of argillaceous deposition. An occasional rufous tinge is due undoubt- 

 edly to the presence of iron peroxide. 



We have on other occasions examined outcrops of limestones at Ansonia, 

 in the valley of the Thessalon,* and near Ottertail, on Ottertail lake, and 

 brief notices of them are here introduced for comparison. The external 

 characters of the Ansonia limestone (IX, 6, 7), especially pinkish samples, 

 are exceedingly like those of the Echo lake limestone ;^but there is a greater 

 amount of flocculent matter, and the calcitic individuals are sometimes large 

 enough to show cleavage cracks. Occasionally they are large enough to 

 give the rock a sparry character (XII, 14). There appear, also, numerous 

 bright green grains, apparently chloritic, and disseminated black opaque 

 specks which appear to be anthracitic. The thin section (IV, 6) is composed 

 of rounded grains, but with a greater frequency of silicious particles. The 

 specimen, however, is not so exclusively fragmental, for there are areas of 

 identical crystalline orientation across which calcitic cleavage may be traced. 

 But these may be only larger fragments of the original material. Some of 

 these sections (IX, 7 ; XII, 11) show the argillaceous banding seen at Echo 

 lake so perfectly that one cannot doubt the identity of the formation. Many 

 examples (XII, 12) from Ansonia have a semi-brecciated structure, with not 

 a little angular quartz; but this condition is evidently due to the action of 

 the dike there present. Other portions of the same specimen pass to the fine 

 condition of the Echo lake limestone. 



The limestone called " lithographic," from near Ottertail (XII, 6), is 

 greenish, excessively fine-grained, weathering buff, with numerous refractive 

 specks disseminated, and also stick-like objects, resembling ground wood- 

 fibers, lying in all directions. In thinnest section the rock structure is 

 fine as that of a precipitate. Oue condition of the Ottertail limestone* 

 439 (XII, 7), is a little brecciated, as at Ansonia. The color is dun as at 

 Echo lake, but near the weathered surface it is dull pink. The lines of 

 sedimentation are distinct and delicate. Disseminated through certain por- 

 tions of the rock are angular and rounded grains of quartz, as also the wavy 

 and fiber-like objects before mentioned. 



The comparison of specimens from Echo lake with others from the Thes- 

 salon valley makes it quite clear that we are dealing with one and the same 

 formation. 



On the other hand, the Bruce limestone, 388 (VIII, 6), is composed of 

 calcitic grains ten times as coarse, without any trace of quartz, and with the 

 interstices filled with decomposition products. Its bedding is much less com- 



* Sixteenth Ann. Rep. Geol. Surv. Minn., 1887, pp. 155, 23-50, and pp. 158, 28. 



