September i6, 1887.] 



SCIENCE. 



141 



solid rock and residuary deposits which so closely resemble the 

 diamantiferous material of the South African mines. 



The accompanying map, introduced, with corrections and ad- 

 ditions, from the United States Geological Survey, Bulletin No. 

 38, shows the distribution of the exposed peridotite and the soil re- 

 sulting from its disintegration. It is only a sketch-map, and does 

 not pretend to a high degree of accuracy, but will be found of great 

 service in the field. 



The embankment, which was formerly regarded as the site of an 

 old furnace, has proved to be an Indian mound in which arrow- 

 heads and fragments of celts have been found. Several years ago 

 the mound was opened to a considerable depth by Mr. James 

 Maggard, who reports ashes near its centre. The excavation made 

 for us during our brief sojourn did not reach the ashes. The 

 mound is composed chiefly of the sand resulting from the disin- 



and are here reported for the first time. When suitably prepared, 

 they will make worthy additions to the gem collection of the Na- 

 tional Museum. They resemble the same transparent mineral from 

 Arizona. The South African specimens of the mineral are a little 

 more opaque, but of a richer green color. 



During a careful search over a small area for nearly two days, no 

 diamonds were found ; but this by no means demonstrates that 

 diamonds may not yet be discovered there. 



The remarkable similarity between the peridotite of Kentucky and 

 that of the Kimberley and other diamond-mines of South Africa is 

 very striking, and, when this alone is considered, the probability of 

 finding diamonds in Kentucky seems correspondingly great ; but 

 when we reflect that the carbonaceous shale, and not the perido- 

 tite itself, is the source of the carbon out of which the diamond is 

 formed, and that the shale in Kentucky is much poorer in carbon 



.Creech 



[xposed Peridatite. gvgnSoU cont*mingPyropc*nd||menJtE. •Fe°dsp«hf#Ro"ks!* 



tegration of the adjacent peridotite, and a number of pieces of 

 peridotite. preserving all their form, but entirely altered with the 

 exception of the garnet and ilmenite, which only appear broken up. 

 The olivine had changed, however, to a deweylite-like mineral, so 

 soft and of such a structure that it has received the local name of 

 ' mutton tallow,' and, when first taken out, can be worked as readily 

 as that substance. 



It is about one hundred feet in diameter and thirty feet in height, 

 and some large trees had originally grown on the top. Until our 

 recent visit the actual contact of the peridotite and shale had not 

 been observed. It is exposed in the bed of a small branch of 

 Isom's Creek, within a hundred yards of Charles Isom's house. 

 The intrusion of the peridotite has displaced and greatly 

 fractured the shale, besides locally indurating it, and enveloping a 

 multitude of its fragments. The latter are dark-colored, like the 

 peridotite, and are strongly contrasted with the light-colored dolo- 

 mitic nodules of secondary origin. 



Besides the pyropes, a few of which are good enough for cutting, 

 several fairly good specimens of a green pyroxene have been found. 



than that of the South African mines, the probability of finding dia- 

 monds there is proportionally diminished. H. Carvill Lewis (Sci- 

 ence, viii. p. 346) remarks concerning the South African mines, 

 that " recent excavations have shown that large quantities of this 

 shale surround the mines, and that they are so highly carbona- 

 ceous as to be combustible, smouldering for long periods when ac- 

 cidentally fired." In the chemical laboratory of the United States 

 Geological Survey, Mr. J. Edward Whitfield determined 37.521 per 

 cent of carbon in the shale from near the Kimberley mine, while the 

 blackest shale adjoining the peridotite near Charles Isom's in Ken- 

 tucky, he found to contain only 0.681 per cent of carbon. After all 

 the carbonates were removed by dilute hydrochloric acid, the residue 

 was combusted in oxygen, and the carbon weighed as carbonic 

 dioxide. The peridotite, at the time of its intrusion, must have 

 been forced up through a number of coal-beds, and at a greater 

 depth it penetrated the Devonian black shale, which is considerably 

 richer in carbon than the shale now exposed at the surface. It is 

 possible, and not improbable, that if the theory of the igneous 

 origin of diamonds first proposed by Roscoe Cohen (Proceedings o£ 



