98 



Marl Underlying Charleston. 



Vol. IX. 



ness in the construction of rods, else we 

 cannot hope for their being generally used. 

 Hence, any appendage that is not decidedly 

 advantageous, ought to be avoided. 



5. "Are not vanes, balls, and ornaments 

 which are often placed on rods, obstructions 

 to the fluid!" 



I think these appendages do not generally 

 affect the efficacy of a rod. 



6. " Should not lightning rods have a 

 clean smooth surface; and would not a coat- 

 ing of iin be beneficial V 



I do not suppose it to be important that 

 the surface should be smooth; but it ought 

 to be free from rust, — which greatly impair 

 the conducting power of iron. A coating of 

 black pamt, — the basis of which is charcoal, 

 (a good conductor,) or, better, a galvanized 

 surface — which is not liable to oxidize, is 

 essential to the permanent efficacy of a rod 



The most essential points in the construe 

 tion of a rod, appear to me to be these: that 

 the rods should project sufficiently high 

 above surrounding objects, and terminate 

 in a bright metallic spinale, — that its parts 

 should have as perfect continuity as possi 

 ble, and that it should descend to the depth 

 of permanent moisture. 



Denison Olmsted. 



Yale College, Sept. 3rd. 1844. 



Marl Underlyiug Charleston. 



E.tlract of a letter from Prof. Bailey of West Point, 

 to Dr. J. Lawrence Smith. 



It may be that the extract from this let 

 ter is of too purely a scientific character for 

 this journal; but it must be interesting to 

 us all notwithstanding, as it is connected 

 with the geological structure of the spot we 

 inhabit; a few preliminary observations will 

 make what follows more intelligible. 



Ehrenberg, a distinguished German natu- 

 ralist, discovered a few years since, that 

 there existed immense beds ot earthy mat- 

 ter miles in extent, and many hundred feet 

 in thickness, formed solely of the remains 

 of microscopic animalcules, so small that 

 millions were comprised within the compass 

 of a cubic inch; their forms are varied, and 

 their composition that of pure sand ; in fact 

 these little creatures v^hen alive, were en- 

 veloped in flinty cells so indestructible as 

 to remain perfect to the present day, a mon- 

 ument of their previous existence; these 

 deposits have been found in many parts of the 

 globe, but no where in greater abundance 

 than in this country. There is a material 

 brought from one of the Northern States, 

 and used as a polishing powder, that con- 

 sists entirely of these remains. Ehrenberg 

 also found chalk to be made up of the re- 



mains of microscopic animalcules, whose 

 covering was composed of carbonate of lime 

 instead of silica. 



These facts which may appear simply to 

 -show the wonders of nature, are destined to 

 be of incalculable service to the geologist 

 in pointing out the comparative ages of 

 many formations upon the globe, and Prof. 

 Bailey of West Point has directed his atten- 

 tion to this subject, his labours have already 

 been of great service; and we look with 

 anxiety to see a complete detail of what he 

 has done in this department of science. The 

 subject of this letter is the immense bed of 

 marl that underlies Charleston, and perhaps 

 a large portion of the eastern half of this 

 State, the thickness of this bed is unknown; 

 it has been penetrated to a depth of over 

 three hundred feet, and the specimens ex- 

 amined were from this boring. 



" You can now inform the good people of 

 Charleston that their city is built upon a, 

 bed of animalcules several hundred feet in 

 thickness, every cubic inch of which is filled 

 with myriads of perfectly preserved micro- 

 scopic shells. The.se shells, however, do 

 not, like those beneath Richmond and Peters- 

 burg, &c., belong to the silicious infusoriae, 

 but are all derived from those minute calca- 

 reous shelled creatures, called by Ehrenberg 

 polythalami. You are aware that Ehrenberg 

 proved chalk to be chiefly made up of such 

 shells, and you will doubtless be delighted 

 to learn that the tertiary beds beneatli your 

 city, are filled with more numerous and 

 more perfect specimens of these beautiful 

 forms, than I have aver seen in chalk or 

 marl from any other locality. These forms 

 are destined to be of great value in geology, 

 and when the precise position of the forma- 

 tion beneath Charleston sliall be fi.xed, and 

 the forms belonging to each bed determined, 

 we shall then have so perfect a guide to the 

 geology of a large portion of our southern 

 country, that by a mere glance through the 

 microscope at portions of strata, scarcely 

 large enough to be seen by the naked eye, 

 their characteristic fossils may be seen, and 

 their true position in the scries determined. 

 It will be a great labour however, to give 

 the subject all .the developement it needs. I 

 iiave myself examined the forms from as 

 many as forty different and distant portions 

 of our continent, but still feel very diffident 

 in using the knowledge thus acquired." 

 "This polythalamia to whose labours South 

 Carolina owes so large a portion of her ter- 

 ritory, are still at work in countless thou- 

 sands upon her coast, filling up harbours, 

 orming shoals, and depositing their sliells 

 to record the present state ot the sea-shore 

 as their predecessors, now entombed beneath 



