" CRYSTALLINE LIMESTONES " OF CANADA. 75 



were deposited the materials of the great crystalline rocks "*, 

 that is, as chemical precipitates. 



There are no more reasons for ascribing the 60,000 feet of 

 Laurentian sands, argills, and other deposits (that is, in their 

 original condition as sediments) to Dr. Hunt's " chemical acti- 

 vities " than there are for attributing the 30,000 feet of similar 

 deposits forming the Longmynds to the same agencies. 



At the Dublin meeting of the British Association, 1878, Dr. 

 vSorby referred to the presence of certain crystalline substances, 

 in the "red clay" and other deposits, which the ' Challenger 5 

 expedition brought up from the bottom of the Pacific and 

 Atlantic Oceans, in such a way as to make it appear that he is 

 ngt opposed to the notion that they are the products of chemical 

 precipitation. The nature of these crystalline substances and 

 the deposits enclosing them is engaging the attention of Renard 

 and Murray. The full result of their investigations has not yet 

 been published ; but some of their conclusions are stated in the 

 British-Association Report of the Sheffield Meeting in 1879, 

 pp. 340, 341. There is nothing in their statements to coun- 

 tenance the idea that any thing in or belonging to the red clay, 

 or the deposit itself, is a chemical precipitate from ocean water, 

 but on the contrary, that it is for the most part a volcanic ash, 

 which through decomposition or disintegration has become con- 

 verted into red clay. The crystalline substances it contains, 

 viz. plagioclase, augite, peridot e, sanidine, magnetite, zeolites, 

 sideromelane, &c., are more probably non-disintegrated portions 

 of mineral aggregations contained in the volcanic ash, than the 

 result of chemical reactions. Prof. A. Geikie (seemingly referring 

 to some of the above), in stating that " these silicates (there may 

 be several of them) have certainly been formed directly on the 

 sea-bottom/ 'f commits himself to what we expect will turn out 

 to be an erroneous conclusion. 



Dismissing the silacid metamorphics for the present, Sterry 

 Hunt's theory of the origin of the Canadian Archaeans in their 

 totality necessarily makes the interbedded " crystalline lime- 

 stones " a " chemical deposit ; and there is no doubt that a part 

 of these limestones, like those of more recent formations, have 

 been directly precipitated by chemical reactions from the waters 



* Nature, August 22, 1878, p. 444. 



t Article " Geology," in ' Encyclopaedia Britannica/ vol. x. p. 288. 



