16 The American Geologist. July, 1897 
have since made known man}' striking exhibitions of the same 
types, especially in the iron-ore ranges of the lake Superior 
region. Among the ore-developments in pre-Cambrian ter- 
ranes, and associated intrusives of that region the prevailing 
modes of occurrence conform to these types. Both kinds of 
replacement are sometimes represented in individual parts of 
connected and related ore deposits, the dominance of one or 
the other in a given locality being governed by relative dis- 
tribution of associated sedimentary and intrusive rocks, or by 
radical differences in origin — whether from essentially calca- 
reous or pyroxenic material. After much elaborate study and 
protracted discussion of the mode of origin of the Huronian 
(Algonkian or pre-Keweenawan) iron-bearing formations of 
the lake Superior region, both folded and structureless, their 
derivation as a rule by epigenesis in situ without sedimenta- 
tion, remains questioned by few among later investigators.* 
Recurring to my previous notice of the so-called Mediter- 
ranean iron ores of Spain and Algiers, f among products of re- 
placement on a large scale upon the evidence of certain 
descriptions of their modes of occurrence, I take occasion to 
remark that they are likewise so regarded by recent observ- 
ers like Mr. Fred. Kensington and Mr. A. P. Wilson, ab- 
stracts of whose original papers have been printed in a report 
by the U. S. Geological Survey. ;J; 
An interesting field for observation of the same class of 
phenomena is presented on certain islands of British Colum- 
bia, visited by the writer in the summer of 1894, namely, Van- 
couver, Texada, and Redonda. 
Of Texada island in the Strait of Georgia, geological de- 
scriptions have been given by Dr. G. M. Dawson and Mr. Rich- 
ai'dson.§ Its topography is well exhibited in several charts of 
the British Admiralty. The predominating rocks of the is- 
land are altered eruptives of the Vancouver series, which are 
*Van Hise, Bull. U. S. Gaol. Survey, No. 86, pp. 170-174. 
tThe Am. Geologist, viii, 1891, p. 374. 
JAnu. Rep. Ill, vol. xvi, pp. 97-99. On the iron ores of ElVja as pro- 
ducts of similar replacement see B.Lotti. 1895, (Zeitsch fiir prakt. Geol.. 
p. 31). J udd's numerous examples of occurrences of the same kind in 
his Geology of Rutland, 1875 (Mem. Geo). Surv. Gr. Br.) were over- 
looked in my original paper. 
§Ann. Rep. Geol. Surv. of Canada, 1873-74; 1876-77: 1886, Part B, 
p. 32. 
