ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 135 



since the minimum is ordinarily several degrees below the 

 freezing point, these factors likewise assist to some extent in 

 the disintegration of the rock surface, especially since the 

 limestone is porous and absorbs a considerable amount of 

 water. However, the St. Louis limestone appears to be able 

 to withstand climatic influences so well that locally it is largely 

 used as a building-stone. While there is a considerable vari- 

 ation in its composition, on the whole it may be said that 

 laboratory tests have shown that the crushing strength of 

 samples subjected to freezing was not seriously diminished.* 

 Hence changes in temperature probably do not greatly affect 

 the rock surface. On the other hand, they serve to pry apart, 

 at the fissure joints, those blocks of limestone which arc situ- 



ated near the surface. 



Geology. 



But few geological or paleontological papers deal ex- 

 clusively with the region or part of the region under discussion 

 and the various publications treating of those parts of Illinois 



Missour 



must be 



Missouri 



Geological Survey, none but the most general features had 

 been recognized, the main interest being centered on the 

 metal, ore and coal producing regions. A summary i 



t 



ppointmcnt 



era, during which were studied not only the different geologi- 

 cal formations, but also the fossils which they contained, 

 something which up to that time had been practically neg- 



lected- 



concerned 



contributed 



largely to a detailed and accurate knowledge of its geology 

 and paleontology. Especially from the standpoint of the 

 Tnf+or spipnnp thp fipld IS pxceodindv rich and attractive, so 



* Buckley, E. R., and H. A. Buchler. The Quarrying Industries of 

 Missouri. Mo. Bureau Geol. and Mines, 2 ser. 2. 1904. 



t Swallow, C. G. First and Second Annual Report of the Geological 

 Survey of Missouri. Appendix A, 1855. 



