GEOLOGICAL CONCLUSIONS. 113 



The bed of chalk referred to was not found on any of the 

 coral islands, bnt in the elevated reef of Oahu, of which reef it 

 formed a constituent part. Jt is twenty or thirty feet in extent, 

 and eight or ten feet deep. The rock could not be distinguished 

 from much of the chalk of England : it is equally fine and even 

 in its texture, as earthy in its fracture, and so soft as to be used 

 on the blackboard in the native schools. Some imbedded shells 

 look precisely like chalk fossils. It consists, according to an 

 analysis by Prof. B. Silliman, Jr., of 



Carbonate of lime, . , , 92-800 



Carbonate of magnesia, , . 2*385 



Alumina, .... 0250 



Oxyd of iron, .... 0543 



Silica, . 0-750 



Phosphoric acid and fluorine, , , 2-113 



Water and loss, . . , 1*148 



The locality is situated on the shores just above high tide 

 level, near the foot of Diamond Hill. This hill is an extinct 

 tufa cone, near seven hundred feet in height, rising from the 

 water's edge, and in its origin it must have been partly subma- 

 rine. It is one of the lateral cones of eastern Oahu, and was 

 thrown up at the time of an eruption through a fissure, the lavas 

 of which appear at the base. There was some coral on the 

 shores when the eruption took place, as is evident from imbed- 

 ded fragments in the tufa; but the reef containing the chalk ap- 

 peared to have been subsequent in formation. There is no cer- 

 tain proof yet ascertained of any connection between the fires of 

 the mountain and the formation of the chalk. 



The facts leave the subject of the origin of chalk still in un- 

 certainty. Its fine earthy texture is evidence that the deposit 

 was not subaerial seashore accumulation, as only sandstones and 

 conglomerates, with rare instances of more con) pact rocks, are 

 thus formed. Sandrock making is the peculiar prerogative, the 

 world over, of shores exposed to waves, either marine or fresh 

 water. We should infer, therefore, that the accumulations were 

 produced either in confined areas, into which the fine material 

 from a beach may have been washed, or on the shores of shallow, 

 quiet seas: in other words, under the same conditions nearly as 

 are required to produce the calcareous mud of the coral island. 

 But, although the agency of fire in the result cannot be proved, 

 it is by no means improbable, from the position of the bed of 

 chalk, that there may have been a hot spring at the spot occu- 

 pied by it. That there were some peculiar circumstances distin- 

 guishing this from other parts of the reefs, is evident; and this 

 appears to be the only probable supposition. If this be admitted, 

 the existence of an elevated temperature might be suggested for 



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