SQo 6N the FORI^IATION OF ROCKS, [Jut}^ 



S9- Siliceous sMsfy (Keiselshieffer) and jasper^ are 

 Jjlaced bere from their resemblance to the siliceous 

 precipitations of the secondary class of Neptunian rocks^ 

 and aKematlng ^vith some of the rocks of the transition 

 class. 



The leading features of the foregoing formations 

 arcj a ttij great extension both in length and breadth^ 

 ill proportion to their depth and thickness^ dividing in- 

 to iiorizontal strata, or at a small inclination, seldom 

 divided by vertical fissures, and continuing through the 

 "wliole strata without any great cliange in the structure 

 or external appearance of the substances. This fonna- 

 tion may he found to occupy generally between the 20th. 

 and 55th, degrees of latitude, Avhilst the primitive may 

 be found to predominate towards the Poles. ^ 



May the proper proportion of heat and moisture, ne- 

 cessary to the production of organic matter, in the mid- 

 dle and santlicrn latitudes, be one reason why we find 

 there tlie foi^mations whicli contain, and are partly com- 

 posed ofj such matter in great abundance ? or tlie ab- 

 sence of heat towards the Poles, be one of the causes 

 "why those formations are not found therein the same 

 ^roporiioK* but consist principally of the piimitivc? 



While little or none of Asia, Africa, and perhaps 

 not one third of Europe, and still less of America, have 

 feeen examined by mineralogists having a knowledge 



* Shoold firtiitpc experience and obsen^atlon demonstrate that Nature has 

 sicciraHifeftesIthegi'ealest propoiiion of tlie secondary formation in the middle 

 and tropical Mittides, and for the same reason continues to heap upon the sur- 

 face in thes/? Mitudes the matter consohdated by the action of animal and 

 Teg-etable Efe; vowld tliis not tend to augroent the diameter of the globe at 

 those places, aiiu of course give the appearance of fiatness to the poles ' 



