80 STUDIES IN GEOLOGY, No. 4 



gen has recorded plant remains associated with Inoceramus 

 in a clay lens in the upper part of the Upper Cretaceous near 

 Colico, but I did not succeed in locating this outcrop. The 

 succeeding Tertiary is everywhere unconformable upon the 

 Upper Cretaceous or older rocks. It consists of a basal con- 

 glomerate of varying thickness overlain by a thick and highly 

 variable series of shales and sandstones with coal seams, and 

 some marine intercalations below the coal carrying species 

 of Fusus, Turritella, Nucula, Lutraria, etc. The coal free 

 portion varies from 146 to 325 feet in thickness and is over- 

 lain by from 300 to 750 feet of shales, sandstones arid grits 

 with several seams of workable coals. These vary in thick- 

 ness and appear to be at very discordant levels in the various 

 mines. The more important have received names and most 

 mines work an "Alta" seam but this is probably not the same 

 seam in the different mines. In fact one gets the impression 

 that the coal seams of workable size are not continuous but 

 much restricted in areal extent. The sandstones are prevail- 

 ingly greenish in tint and crossbedding is frequent. This is 

 borne out to a certain extent by drill cores examined at 

 Colico where a short distance from the present mine the 

 drill had penetrated 1,100 feet of essentially uniform grits 

 without encountering either shales, coal, or marine fossils. 

 A good idea of the detailed variations of the Tertiary section 

 for comparison with the above can be obtained from the 

 Coronel section described in 1870 by Lebour and Mundle. 12 

 A fauna of the same general facies as that below the coals, 

 but more abundant, is found in intercalated lenses through a 

 considerable thickness in the superior non coal bearing part 

 of the section. This fauna, comprising species of Nucula, 

 Mytilus, Sole n, Tellina, Limopsis, Glycimeris, Panopea, Ve- 

 nus, Pinna, Dentalium, Oliva, Cassis, Natica, Fusus, Cancel- 

 laria, Bulla, etc., is in the main the so-called Navidad fauna 

 that has been recorded from numerous localities along the 

 Chilean coast. It is clearly Miocene in age but in its entirety 



"Lebour and Mundle, Geol. Mag. dec. I, vol. 7, pp. 499-509, 1870. 



