104 ON TIFE TOrOGltArilY AND CiEOLOGY 



the small solitary forms are almost unknown. Again, a mass of madrepore is some- 

 times seen inbeddecT in the matrix and isolated from all companions. But the great 

 bnlk of the rock is a very soft light cream-colored chalky material, the comminuted 

 debris of coral, &c., such as is forming at the present day among the coral reefs of 

 the Bahamas and Bermudas.* The local name of this material in Santo Domingo is 

 " Caliche." It has the peculiarity that it hardens on exposure to the atmosphere, 

 though not always to the same extent. Usually in natural exposure this hardening 

 takes place to a depth of from two to four feet, though often the crust is not more 

 than a foot thick. The indurated portion is sufficiently solid for building purposes, 

 although it is almost invariably penetrated in all directions by small cavities, caused 

 partly by the decay of the enclosed fossils. In some cases this shell is so tough that 

 the pick hardl}^ makes an impression on it, and it is necessarj^ to use powder in 

 quarrying it. It makes an excellent lime and is burnt in kilns of about three hun- 

 dred barrels capacity, the loose surface blocks being preferred for the purpose, the 

 softer material not having sufficient consistency for the kiln. Almost the entire city 

 of Santo Domingo is built of this rock, and buildings of thi'ee centuries old attest 

 alike the durability of both the stone and the mortal'. 



The soft " caliche " hardens rapidly on exposure and although as soft as clay when 

 quarried makes an excellent road material. It makes a hard, smooth road, not wearing 

 easily into ruts, but liable to be cut by running water. Even the harder material 

 soon grinds down under wdieel and hoof to an uniform surface, whose only objection is 

 that its nearly white color is too dazzling to be pleasant to the e3^e, though it is not 

 so bad as the painfully brilliant glare of the streets of jN^assau, where at mid-day 

 only strangers and dogs are to be seen in the street." 



The origin of this rock is at least in part suffieientl}^ obvious. The whole deposit 

 seems to be homogeneous. 'No signs of stratification or differences in degrees of 

 hardness being perceptible below the above-mentioned crust. There can be no 

 question Imt what the greater part is derived from the corals and the few shells which 

 lived, died, and decayed on the spot, I^elson after several years of investigation in 

 the Bermudas, arrived at this result, attributing the origin of the Bermuda "chalk" 

 entirely to this cause.f 



* See Nelson, Quart. Jour. Geol. Society, Vol. IX., p. 207, 208, also Trans. Geol. Soc, Vol. 5, part 1, p. 104 & 105. 



f Trans. Geol. .Soc, Vol. 5, part 1, p. 114, * * ■•. "But from all that I have seen during different examinations of 

 decomposing zof)phytes a.nd shells * I have no more hesitation in attributing the existence of the Bermuda chalk 

 to such a source than I have for asserting that llie obvious material of the Bermuda stone is derived from the same 

 origin ; with, iiowever, this difference that in the latter instance the fragments are the result of mechanical subdivision, 

 while iri the former the elementary particles are due to the decay by long submersion of the membranous tissue, 

 which pervading their whole structure, releases the constituent calcareous matter dispersed through the texture, 

 when it is ruined by decomposition." 



