6(j ME. 0. H. EVANS ON THE [Feb. I907, 



When examined more closely, the Taltal shell-beds present some 

 interesting features. I will take those of Punta Taltal as an 

 illustration. 



Punta Taltal was formerly an island of igneous rock, separated 

 from the mainland by a strait some hundreds of feet wide. The 

 gap is now bridged over by a raised beach, consisting of entire and 

 broken shells, covered with a layer of big rounded boulders, the 

 whole indurated by a calcareous cement derived from the decom- 

 position of the shells. Bones of the whale are by no means 

 uncommon in this deposit. Throughout the bed, the different 

 genera of molluscs are curiously localized • thus, one part consists 

 mainly of Pecten, another of Oliva and Turritetta, while elsewhere 

 Concholepas or Pectunculus may predominate. An important 

 feature is, that many of the lamellibranchs have their valves united 

 as in life. The commonest shell in the modern and ancient beaches 

 is the Concholepas. Certain shells, more particularly the Olivce, have 

 their substance entirely converted into crystalline calcite exhibiting 

 its characteristic cleavage. A curious change has taken place in 

 portions of the lower beds, where they are exposed to the action 

 of spray from the heavy breakers. Here, in many instances, the 

 shell itself has been removed, and replaced by a delicate internal 

 cast, so sharply taken that the faintest markings of the vanished 

 valve are perpetuated, even to the delicate impressions of the 

 polyzoa that formerly grew within it. In the case of the Turrittllce 

 the effect is reminiscent of the Portland ' screw-stones/ 



It is very noteworthy that some of the fossils are actually replaced 

 by internal casts of saline matter, with which, as I have said, the 

 formation is impregnated. These curious pseudomorphs are rather 

 scarce, and, being quite soluble in water and very fragile, seem to 

 have owed their preservation to the shelter afforded by big 

 boulders from percolating rain-water. Lower down in the same 

 section there was much gypsum, and here the mass becomes very 

 hard. Most of the shells are bleached quite white, but even in 

 the older beaches at a high elevation, shells resembling Ghlorostoma 

 retain their colour. 



The upper layer of rounded boulders gives rise to strange forms 

 where subjected to marine erosion. Along the cliff, for a consider- 

 able distance, the boulder- bed overhangs the sea in an inclined 

 ledge; and, where portions of the raised beach are isolated, they 

 assume a mushroom shape, a broad cap of the conglomerate being 

 left supported by a comparatively-slender pillar of indurated shelly 

 matter. 



In his * Geological Observations on the Coast of South America ' 

 Darwin 1 described a rock in the calcareous beds of Coquimbo, 

 locally known as ' losa,' as consisting of minute hollow capsules, 

 showing evidence of having been formed round fragments of shell. 

 This feature is well exhibited in some of the Taltal raised beaches, 

 where the material is locally made use of, to a small extent, to form 



1 2nd ed. (1876) chap, ix, p. 248 ; also chap, vii, p. 162. 



