tlELATlON OF THE OlLS TO STtlUCTUiElE 641 



Table III. — Principal Oil Structures (Dynamic) 



Class of structure. 



Anticlinal 



(in wet sands). 



Synclinal j 



(in dry sands), i 



Honioclinal. ^ 



Aclinal (fiat; 



Structural units. 



Geanticline. 



( Isolated. 

 Anticline. -| Associated with 



( synclines. 

 Intersecting anticlines, 

 rv f Normal. 



D^^^^^-i Salt domes. 



Geosyncline. 



( Isolated. 

 Syncline. \ Associated w i t h 



( anticlines. 

 Intersecting synclines. 

 l>o\vl-shaped depressions. 



An.ti-homocliiie 



(convex surface). 

 Syn-homocline 



(concave surface). 

 Plane-homocline 



(plane surface). 



Absent in Appalachian field. 



Subordinate structures. 



Bulges on crest, 

 j Plunging ends. 

 1^ Spurs 

 r Struclnral terraces. 



Saddles (l)etween synclinal 

 depressions on same axis. 



Depressions in bottom. 

 i Axial plunge lines. 

 ' Lateral sags 



Structural terraces. 



terr 



aral (Dip 

 Aces. 1 Dip 



flat. 



Original structures only. 



A word may be said regarding the terms "homoclinal" and "aclinal/^ 

 Homocline is a term introduced by E. A. Daly^^ for a dip in one direc- 

 tion, but not necessarily of like degree at all points, as in a monocline. 

 Anti-homocline hcas been used to designate a homocline of convex surface 

 and syn-homocline one of concave surface.^^ Monocline is restricted by 

 Daly and otliers to drops or one-limbed flexures in flat or slightly in- 

 clined rocks. Acline has been used to designate flat-lying beds — that is, 

 without dip. 



RESERVOIRS 



Of equal importance to structure is tlie character of the reservoirs. 

 Many different classifications have been proposed. That followed by the 

 writer is given in the accompanying table, page 642. 



It hardly needs to be said that the metamorphic and igneous classes of 

 reservoirs are of scientific rather than practical interest, so far as the Ap- 

 palachian oil field is concerned. Oil has been reported in igneous rocks 

 at the contact with sedimentaries in Quebec, in basalts in Mexico and 

 Oregon, and in granite in AYyoming, and may likewise b^ expected under 



1" Canadian Dept. of Mines, Geol. Survey, Memoir 68, p. 5.3. 

 " Johnson & Huntley : Ibid., p. 64. 



