14-7 



1885.1 [Cope. 



taceous age. This limestone lies elevated at a high angle against the trap- 

 dyke, at a point on the San Miguel creek ; showing, first, that the trap 

 formation is a dyke which has been thrust up from below, and is not an 

 outflow ; and second, that the age of the elevation of the dyke is later 

 than the Cretaceous period. This conclusion is all important in the deter- 

 mination of the age, and, therefore, probable quality of the coal, and in 

 the determination of its quantity. 



The coal formation lies horizontally bedded in the intervals between the 

 trap-dykes and the hills of limestone, etc. It consists of regularly strati- 

 fied beds of clay, of volcanic ash, of clay or carbonaceous shales, more or 

 less finely bedded, and of thicker and thinner beds of a frequently very 

 good lignite coal. There are no beds of stone in them, but the carbo- 

 naceous shales are frequently very tough. The bedding has not been 

 affected by the dykes, and indeed sometimes inclines downwards towards 

 them at a low angle, instead of upwards towards them as would have been 

 the case had they been older than the dykes. Further evidence that the 

 coal formation is newer or of later age than the dykes is seen in the fact 

 that beds of coal are found in some localities on top of them. It follows 

 from these facts that although there are beds above the dykes, there is no 

 coal below the precipices which constitute the parts of the dykes which 

 are visible ; or, in other words, that the coal only occupies the spaces be- 

 tween the dykes. Fossil mammalian remains found in the beds of clay 

 near the coal prove that the formation is of Upper Miocene Tertiary age, 

 and perhaps identical with the epoch known in North America as that of 

 the Loup Fork.* 



The properties which I examined bear the following names : Galiana, 

 Hulla, Juarez, Concha, Providencia, Capa Rosa, Sausz, San Miguel and 

 San Rafael. I take them up in order. I premise by saying, that the coal 

 beds have been rendered accessible by the erosion of the middle parts 

 of the valleys which they occupy, into deep ravines. The coal outcrops 

 are on the sides of these ravines, and extend underground to a line which 

 descends vertically continuous with the faces of the trap precipices, at 

 which point they are cut off by the concealed part of the dyke. The 

 amount of coal is of course to be determined from this dimension, i. e., the 

 distance from the dyke multiplied by the extent of the formation parallel 

 to the dyke, by the thickness of the bed. 



The coal beds are best exposed on the Galiana property. From 

 the top of the trap dyke to the bottom of the valley at this point, 

 the vertical depth is about one thousand feet. At a depth of about 

 100 feet from the summit of the hill is a short, open cut in which 

 can be seen a bed of good coal of eighteen inches in thickness. 

 From its position, this bed probably extends entirely across the sum- 

 mit of the hill, and crops out on the other side, forming the San Rafael 

 mine. Below this open cut the summit of the trap precipice is soon 



*See American Naturalist, May, 1885, where this fact is stated. See also de- 

 scription of fossils at end of this article. 



