22 EARLY LETTERS [CHAP. I 



Letter 6 which I believe is the Gryphcza is the most abundant an 

 Ostrea, Turmtella, Ammonites, small bivalves, Terebratulcz (?). 

 Perhaps some good conchologist x will be able to give a guess, 

 to what grand division of the formations of Europe these 

 organic remains bear most resemblance. They are exceedingly 

 imperfect and few. It was late in the season and the situa- 

 tion particularly dangerous for snow-storms. I did not dare 

 to delay, otherwise a grand harvest might have been reaped. 

 So much for the western line ; in the Portillo pass, proceed- 

 ing eastward, we meet an immense mass of a conglomerate, 

 dipping to the west 45, which rest on micaceous sandstone, 

 etc., etc., upheaved and converted into quartz-rock penetrated 

 by dykes from the very grand mass of protogine (large 

 crystals of quartz, red feldspar, and occasional little chlorite). 

 Now this conglomerate which reposes on and dips from 

 the protogene 45 consists of the peculiar rocks of the first 

 described chain, pebbles of the black rock with shells, green 

 sandstone, etc., etc. It is hence manifest that the upheaval 

 (and deposition at least of part) of the grand eastern chain 

 is entirely posterior to the western. To the north in the 

 Uspallata pass, we have also a fact of the same class. Bear 

 this in mind : it will help to make you believe what follows. 

 I have said the Uspallata range is geologically, although 

 only 6,000 7,000 ft., a continuation of the grand eastern 

 chain. It has its nucleus of granite, consists of grand beds 

 of various crystalline rocks, which I can feel no doubt are 

 subaqueous lavas alternating with sandstone, conglomerates 

 and white aluminous beds (like decomposed feldspar) with 

 many other curious varieties of sedimentary deposits. These 

 lavas and sandstones alternate very many times, and are 

 quite conformable one to the other. During two days of 

 careful examination I said to myself at least fifty times, how 

 exactly like (only rather harder) these beds are to those of the 

 upper Tertiary strata of Patagonia, Chiloe and Concepcion, 

 without the possible identity ever having occurred to me. At 

 last there was no resisting the conclusion. I could not expect 

 shells, for they never occur in this formation ; but lignite or 

 carbonaceous shale ought to be found. I had previously been 

 exceedingly puzzled by meeting in the sandstone, thin layers 



1 Some of these genera are mentioned by Darwin (Geol. Obs., p. 181) 

 as having been named for him by M. D'Orbigny. 



