12 PROCEEDINGS OF THE COLUMBUS MEETING 



seen in them and, more rarely, a fragment of Bilicified wood. The slates, shales, 



and finer sands which make up the other beds are extremely variable, and their 

 characters have been very well described by Aguilera.* This variability makes it 

 extremely difficult to trace the beds with certainty, since a clay slate may pass 

 into a sandy slate or bedded sand, or a sandy slate into a coarse massive sandstone 

 in a comparatively short distance. 



The slates are extremely rich in plant remains, which are well preserved, and 

 many of them very beautiful. So far as I know, they have only been studied 

 slightly as yet. Sefior Aguilera gives a list of those noted by Doctor Newberry 

 and a few others determined later,' and I sent a small collection to Dr I. C. White, 

 which was given to Professor Win. M. Fontaine, who writes me as follows: 



" Tlic plants that Professor Whit" sent some time ago .-is coming from you and obtained in Mexico 

 certainly conic from a horizon well up in the Mesozoie. Most if not all of them seem to lie new 

 species. That and their small number make it not possible to give with certainty the exact hori- 

 zon. To judge, however, from them, it, appears to he the uppermost Trias or Rhetic. They im- 

 press me as being of about the age of New berry's Abiqua copper mine plants, or those of the older 

 Mesozoic of Virginia and North Carolina." 



In addition to these plants in the shale and thin bedded slates, the more massive 

 slates carry siliciiied stems and branches of shrubs, and the finer grained bedded 

 sands trunks of trees up to more than a foot in diameter. In grain these latter 

 resemble the elm. 



None of the beds show cross-bedding to any extent. 



Each prominent bed of slate and shale seems to have one or more seams of coal 

 in it, and, although like Triassic coals in general, the deposits may be more or less 

 lenticular, nearly all of these beds are workable somewhere along their extent in 

 this territory. 



The limestones are only occasionally present and generally near the top of the 

 division. They are usually very argillaceous, but sometimes more calcareous. 



Only a few localities have yielded fossils other than plant remains. Previous to 

 this examination the only marine fossils known were those from San Marcial, ()0 

 miles west of this locality, described by Meek in volume 1 of the Paleontology of 

 California. So far I have not found here the forms described by him, but in a 

 band of limestone I find, as imprints, a great number of other forms of marine in- 

 vertebrates which have not yet been studied. 



The only member of the Lista Blanca present in this immediate field is the heavy 

 agglomerate, the basal conglomerate not appearing unless it is represented by the 

 ferruginous quartzitic breccia placed in the Barranca division. It presents no fea- 

 tures different from those already described.! It lies with apparent unconformity 

 on the Barranca, but is involved with that division in its various flxeures. 



The two sections given represent the general relations of the beds in each of the 

 two areas with what seems to us the probable connection. If this be correct, they 

 represent fully the variability of the beds in longitudinal extent as described by 

 Sefior Aguilera. 



The regularity of these beds is much disturbed by intrusions of igneous rocks. 

 This rock, which is principally trachyte, has been forced along the bedding planes 

 of the slate or between the slate and coal for long distances. In places it may be 

 only a foot or two in thickness, and on weathered faces so closely resemble a bed 



*Op. fit. 



fTrans. American Institute of Mining Engineers. 



