868 



APPENDIX. 



PAGE FIG. 



641 1076, 1077 Author. 



644 1078 ! Holmes. 



645 1079 ! . .Powell's Exped. photograph. 



646 1080 Ives. 



651 1081, 1082 Lesley. 



652 1083-1092 Lesley. 



659 1092 U\ S. Coast Survey. 



661 1093 Richthofen. 



666 1095 Vanuxem. 



677 1096, 1097 Author. 



681 1098 ! J. D. Hague. 



ftQn ( 1100! Guvot (in part). 



DJU j 1101-1104 ". . . . Tvndall. 



690 1105 Agassiz. 



700 1106 Holmes. 



708 1108 Photograph by Jackson. 



724 1110 Author. 



725 1111, 1112 Author. 



726 1113-1115 Author. 



7qft (1116 Author. 



/ou I 1117 ! Coan and Judd. 



735 1118 Photograph by Watkins. 



740 1119 Author. 



PAGE 



741 



742 

 750 

 751 

 752 

 772 

 773 

 779 

 786 

 787 

 788 

 789 

 790 

 792 



793 



794 

 799 

 801 

 802 

 803 

 840 

 852 



FIG. 



1120. J. D. Whitnev. 



1121 Holmes. 



1123-1125. .Photographs bv Jackson. 



1126 Holmes. 



1127 Photograph. 



1129 De la Beche. 



1130, 1131 De la Beche. 



1132, 1133 Crouch. 



1134 J. L. Campbell. 



1136-1141 Author. 



1142 Author. 



1143 Holmes, Gardner. 



1144 J.M. Safford. 



1145 Powell. 



1146, 1147 Powell. 



1148-1150 Heim. 



1150 A! Author. 



1151, 1152 Townsend. 



1153-1156 Daubree. 



1157 '..Daubree. 



1158 Daubree. 



1160 G. K.Gilbert. 



1161, 1162 Marsh. 



The Plates 1 to 12 are all from O. C Marsh. The Physiographic Chart is by the 

 Author, excepting the Topograph}' of the Continents by A. Guyot. The dark lines 

 over the dark-shaded parts of the Continents indicate the courses of mountain ranges 

 or chains. The dotted lines crossing the oceanic areas are isothermal lines, passing 

 through points having the same mean temperature for the coldest month of the year 

 (and hence called isocrymes), and the number attached to each marks the mean tem- 

 perature in Fahrenheit degrees. The line A A crossing the Pacific Ocean obliquely 

 gives the direction of the longer axis of the Pacific Ocean ; and B B in the North At- 

 lantic Ocean, the same for that ocean. The line A/ A' in the Pacific is the axis of the 

 area that was affected by the Coral-island subsidence. 



The oceanic zone between the isothermal lines (or isocrymes) of 68° F., which is col- 

 ored pale yellow, is that over which the temperature is favorable for the growth of reef- 

 forming corals; and outside of it the temperature excludes them. 



F. — Suggestions for the Working Geologist. 



1. Diagrams of Sections. — Uniformity in the mode of representing the several kinds 

 of rocks in diagrams of sections, would avoid the necessity of explaining that this part 

 stands for sandstone, that for limestone, and so on. The modes exemplified in the sec- 

 tion on page 102 have the advantage of being simple and self-explaining. Limestone 

 is represented by a blocked surface, as opposite Trenton; shale, by fine lining, as oppo- 

 site Utica and Hudson River; sandstone of different degrees of fineness, by dots of dif- 

 ferent degrees of coarseness ; laminated or shaly sandstone, by cut lines or a combina- 

 tion of short lines and dots, as opposite Salina and Hamilton ; conglomerate, by very 

 coarse or open dots, as opposite Millstone-grit. 



2. Tilted or Folded Bocks. — In studying a region of tilted rocks it is important that 

 the dip and strike should be obtained at all outcrops, and noted down on a map. For 

 the latter, the best mode is to use a symbol like the letter f, giving the top the direction 

 of the strike and the stem that of the dip ; and the different angles of dip may be ap- 

 proximately indicated by variations in the length of the stem of the T, as in the an- 

 nexed figure, in which the ratio of the stem to half the top of the T is for 80° = 1: 4; 





90° 



70° 60° 



50 c 



45° 35° 



25° 



15° 



