APPENDIX. 



A. — Suggestions for the "Working Geologist. 



1. Diagrams of Sections. — With uniformity among geologists in the mode of repre- 

 senting the several kinds of rocks in diagrams of sections, it would not be necessary with 

 each such section to explain that this part stands for sandstone, that for limestone, and 

 so on. The particular modes exemplified in the section on page 102 have the advantage 

 of being simple and self-explaining. They consist in representing limestone by a 

 blocked surface, as opposite Trenton or Lower Helderberg, in the section referred to; 

 shale, by fine lining parallel with the bedding, as opposite Utica and Cincinnati; sand- 

 stone of different degrees of fineness, by dots of different degrees of coarseness; laminated 

 or shaly sandstone, by cut lines or a combination of short lines and dots, as opposite Sa- 

 lina and Hamilton; conglomerate, by very coarse or open dots, as opposite Millstone-grit. 

 Also, for a schist (as mica schist or gneiss), in the manner illustrated on page 213. 



2. Tilted or Plicated Rocks. — In studying a region of tilted rocks with clinometer in 

 hand, first, after finding, over the upturned edges, a place where the edges are quite hori- 

 zontal, or marking carefully on the tilted surface a horizontal line, take the strike ; 

 then, the amount of dip, noting also its general direction (its precise direction being at 

 right angles to the strike). From the note-book, put the observation on a map by means 

 of a symbol shaped like a letter T> the top having the direction of the strike, and the 

 stem that of the dip, the length of the stem being shortened as the dip increases. Mul- 

 tiply the observations until the map is covered with T's. Their positions on the map 

 will indicate all anticlinals and synclinals, the meeting of two, thus H \~, indicating the 



former, and thus I 1, the latter. Where the strata are vertical, the T would become 



a straight line; and, where horizontal, a cross thus, +• The angle of strike and dip can 

 be written with each T on the map, in very fine letters. 



In all cases, especially those of high dip (40° and upward), wherever faults or folds 

 are a possibility, question their existence until their absence is fully proved, or the con- 

 trary; and, when proof cannot be obtained, doubt. Be careful not to let local flexures 

 obscure the truth with regard to the general folds of the region. Note, also, that, where 

 the dip is small, the variations in the strike are often great; and that a careful compar- 

 ison of all the results over a wide range of country, and of the bendings indicated, may 

 be necessary, to ascertain the true direction of the axis of elevation. 



It is, moreover, important to have in view, in the study of plicated regions, that the 

 beds were once horizontal, and have been warped out of horizontality by lateral pres- 

 sure ; and that, therefore, the warpings or flexures, although obscured by faults, must 

 be compatible with one another. 



Note, also, that limestone is as solid when first made and consolidated, as at any time 

 afterward, as exemplified by the coral limestone of Coral Islands; and that thick strata 

 of limestone — the thickness a thousand feet or more — are very resistant to flexure 

 before lateral pressure, while shales ma}' bend and fold easily. 



Note further, that the mountain ridges of a region are more probably synclinals than 

 anticlinals, the rocks of an anticlinal breaking and yielding easily to denudation, while 

 those of a- synclinal are pressed and compacted together, and put in a condition to resist 

 denudation. 



