Origin of the Grand Outline Features of the Earth. 391 
[. rte ‘f 
/ ( We, 
/ 0 7 4 A 
BY wer re le px a 
bs he dikes (courses of fissures) have the following character- 
ICS :— a 
1. A general uniformity of direction. | 
2. A situation in several parallel ranges. ve } 
3. An interrupted character, and a frequent advancing or re~ 
ceding in the successive parts of a line, or an overlapping of the 
extremities, as in figures 1, 2, 4, 5, constituting what Dr. Perci- 
val has well designated “advancing,” “ receding” or “contin- 
, es. 
ued” seri 
4. Curved lines; some simple, others composed of several 
Straight lines, and others of subordinate curves. 
- Various irregularities in the lines, and deviations from par- 
allelisms, although belonging to the same general system. 
