SLATE CONGLOMERATES AND LIMESTONES. 121 



lake. This vicinity is appropriated, on Logan's map, to the upper slate con- 

 glomerate ; but, as we have shown, the upper slate conglomerate terminates 

 three miles south and is followed by felsites and felsitic quartzites, and this 

 is, therefore, the lower slate conglomerate. Logan has located a " supposed 

 outcrop of limestone" to the north of this, and has connected it with the 

 Echo lake limestone toward the west, and extended it as far as Wahbique- 

 kobing lake on the east ; and then, by the manipulation of supposed faults 

 in the valley of the Thessalon, has caused the limestone to reappear nearer 

 the coast and pass into the observed position of a limestone back of the 

 Bruce mines. The Bruce limestone should then be identifiable with the 

 Echo lake limestone-^ question which we shall presently examine. In the 

 intervening distance between these two branches of the limestone belt desig- 

 nated " 3e," Sir William locates the similar branches of a calcareous forma- 

 tion designated " 3^, Yellow chert and limestone." This is represented as 

 coming between two quartzites, as " 3e " is put down between two slate con- 

 glomerates. The whole geologic structure is worked out with consummate 

 ingenuity on the assumption of faults in such places as would be necessary 

 to produce the results depicted on the map. That a synclinal exists along 

 the Thessalon valley it is easy to admit after an examination of the comple- 

 mentary dips. That the assumpti(m of faults would afford easy explanations 

 of phenomena as identified and understood by Logan will not be disputed. 

 But to us who have studied a considerable part of the field, the numerous 

 Logan faults appear a heavy tax on credulity and introduce what appears 

 an artificial complexity in the geology of the region. It is admitted, how- 

 ever, that one or more faults probably exist — possibly all those laid down on 

 the map. 



Now, it was the opinion of Mr. Murray that the Echo lake limestone 

 trends more to the southeast than Logan has represented, and makes con- 

 nection with the limestone of Ottertail lake and Thessalon river, and, by 

 means of a flexure, with the Bruce limestone also. Our petrographic exam- 

 inations show that Murray was probably correct. 



Microscopic Characters of Echo Lake Rocks. — Thin sections of the limestone 

 from the western side of Echo lake (XXVI, 11 and 12) * show it to consist 

 of very fine rounded grains of calcite, mostly quite refractive and showing 

 extinctions on rotation. The grains are closely compacted, with very little 

 interstitial matter. The dark linear bands are composed of matter of decom- 

 position ; apparently an argillaceous residuum after the solution of the cal- 

 careous matter of some portion of the original material. The rock contains 

 occasional minute grains of quartz. This limestone is evidently fragmeutal, 

 formed of grains of an older crystalline mass ; at least of crystal fragments 



*Our examples of these limestones are registered as follows, the numbers in parentheses refer- 

 ring to thin sections: Ansonia, 409 (IX, 6), 410 (IX, 7), 449 (XII, 11), 450 (XII, 12), 452 (XII, 14; 

 Ottertail, 438 (XII, 6). 439 (XII, 7); Bruce, 388 (VII. 6); Echo lake, west side, 1092 (XXVI, 11), 

 1093 (XXVI, 12), 1095 (XXVI, 13), 1107 (XXVI, 16); Echo lake, east side, 1096 (XXVI, -) ; Garden 

 river, 1108 (XXVI. 14). 



