Geological Results of the Earth's Contraction. 91 



the tension causing fractures would be exerted with some reference to 

 the structural lines, the tension and the structure being both a simulta- 

 neous consequence of cooling, (iii, 394.) 



b. Direction of fissures modified by the relative positions of the large 

 areas of unequal contraction, and whatever the actual course, frequently- 

 attended by transverse fractures, (iii, 395, 396.) 



c. As the force of tension acts tangentially in a great degree, (like 

 the pressure of stone against stone in an arch, and that of the whole 

 arch against the supporting or confining abutments,) the effects will ap- 

 pear either over the subsiding area, or on its borders ; and they will be 

 confined to the latter position whenever the surface is strong enough to 

 resist fracture, (iii, 96, 97, 181, 395.) 



d. The borders of large subsiding areas sooner or later experiencing 

 deep nssunngs and extensive upliftings through the tension or horizontal 

 force of the subsiding crust; these upliftings frequently in parallel se- 

 ries, of successive formation, or constituting a series of immense paral- 

 lel folds; that side of the fold in general steepest which is most remote 

 from the subsiding area, (iii, 98, 182, 186.) 



e- Fissures formed having the character of a series of linear rents 

 either in interrupted lines or parallel ranges, instead of being single un- 

 broken lines of great length, and this owing to the brittle nature and 

 structure of the earth's crust ; ranges sometimes curved, either from 

 having a general conformity to the outlines of contracting areas, or be- 

 cause proceeding from an inequality of force along parallel lines of ten- 

 sion over a subsiding area,* (iii, 185, 385.) 



IV. Escape of heat and eruptions of melted matter from below 

 through opened fissures. 



fl - Igneous ejection of dikes an effect and not a cause of displace- 

 ments, (iii, 99, 185.) 



( *• Some points in the wider fissures continuing open as vents of erup- 

 tion. The outlines of large contracting areas being liable from the 

 cause just stated to deep fissurings, these therefore likely to abound 

 most in volcanic vents, (iii, 98, 186.) 

 c - Heat from many fissures giving origin to hot springs. 



The writer would remark here, in order not to be misunderstood, thai in ic- 

 counting for curving ranges of elevations, or courses of fissures, by the lateral 

 wee of a subsiding crust, (iii, 395,) he has considered the smaller circular areas of 

 ■gftwnii action alluded to, as producing scarcely appreciable results, eieept when 

 combined in lar^e compound areas which subside as a whole. The great curves 

 on the east and northeast of Asia, in the mountains of the continent, as well as in 

 Wie ranges of islands, are not n< arily due to each being the outline of a cir- 



J'nr area of contraction, although we cannot deny that instano of thfis are po> 

 "■*«; but rather to the subsidence that deepened" the Pacific depression, and its 

 u n«qual amount in different transverse lines, connected with the structural char- 

 aner of the crust or its courses of easiest fracture, (iii, 185:)— for these curves are 

 "" c °»- dike toicnnls the. ocean, and similar also are the subordinate cur s in 

 N k Im,ies > (««<* *J that by Negros, West Mindana* and the Sooloo Sea to 

 :? 0rth Borneo, and that by East" Mindanao, Sangir and North Celebes,) as well as 



e CUrVes in the mmmtnini nf Eaati>rn Aiiatrniia. (iii. 388.) 







