The Cylindrical Structures in Lanark County reported in Jean Dugas’ 1952 Doctoral Thesis

In my  August 27, 2015 blog posting I mentioned that Jean Dugas,in the notes to geological  Map 1089A, reported that cylindrical or conical structures in sandstone can be found in North Elmsley Township,  Lanark County.   He commented:

“Peculiar bands showing cylindrical or conical structures noted in the Nepean formation, and best observed on lot 24, Con. VI, North Elmsley tp., are the same composition as the surrounding sandstone , but cut sharply across the beds and are themselves bedded parallel with the walls of the structures.  They are probably formed by slumping of the sand due to water action.”

Morley E. Wilson and Jean Dugas, 1961,
Map 1089A, Geology, Perth, Lanark and Leeds Counties, Ontario, Geological Survey of Canada; Geology by Morley E. Wilson, 1930 and Jean Dugas, 1949; Descriptive notes by Jean Dugas.
                 
In my August 27, 2015 blog posting I also mentioned that I had not been able to find  Dugas’ occurrence on Lot 24 or his thesis.

I  recently located and read Jean Dugas’ doctoral thesis:

Dugas, Jean, 1952,
 Geology of the Perth map area, Lanark and Leeds Counties, Ontario; Ph. D., McGill, 189 pages, four  maps.          

In his thesis he includes five clear  photographs of the conical and cylindrical structures, and good written descriptions of the structures, together with a review of the leading papers discussing theories for their origin.  He concludes that his structures, because of their conical shape, were formed by slumping, and suggests that “as most of the structures are underlain by [crystalline] limestone and it is common to find solution cavities in the [crystalline] limestone” the slumping was likely into cavities in the limestone.

Interestingly, while the the captions to his photographs place the structures on lot 24, the  text of Jean Dugas’ thesis mentions that the structures are found on lot 23.   Both the text and the captions place the structures in concession VI.  In the text of his thesis he comments (at page 99):
      
"Good exposures of an unusual structure in the Nepean sandstone can be seen on lot 23, concession VI of North Elmsley township. A section of the sandstone shows a decisive break in bedding. Across the stratification, two conical structures occur with the apex down, about six feet high and five feet at the base of the cone (cf. photos nos. 29,  30,  31, p. 100). There is a distinct irregular banding, the bands being slightly twisted (cf. photos nos. 31, p. 100, and 32, p. 101). In horizontal section the structure is obviously concentric, forming a circle or a spiral (cf. photo. no. 33 , p. 101).  Though no other exposures of vertical sections have been found, concentric layers were observed at other places in the sandstone.”

Lots 23 and 24 of Concession VI in North Elmsley Township are a few kilometers west of Rideau Ferry and lie south of County Road 1.   Perhaps armed with the photographs I will have better luck locating the outcrops, particularly if I look in both lots.

Christopher Brett
Lanark County