294 W. H. HOBBS — GUADIX FORMATION OF GRANADA, SPAIN 



explain on the theory of marine origin for the great sandstone formations. 

 The enormous expanse of sandstone formations fits better to a desert 

 than to a marine theory of origin along the ocean borders. In the Tri- 

 assic or Newark formation we find beds of clay of clastic origin lacking 

 marine fossils, together with conglomerates, moraine-like deposits of 

 debris, great beds of sandstone and conglomerate, colored clays, and beds 

 of salt and gypsum, all alternating with marine sediments. Within the 

 sandstones are found rain-drop impressions as well as footprints of ani- 

 mals, but without the animals themselves. 



In the Tertiary deposits of the Paris basin there is found such an 

 alternation of marine sediments filled with mollusks, with clay, gypsum, 

 and sandstone, including the bones of land animals, that it is little wonder 

 Cuvier was impelled to adopt his theory of earth cataclysms to explain 

 them. Just such alternations are, however, characteristic of the deposits 

 in desert regions, where the torrent and the playa lake are found, where 

 the surface deposits are continually shifted by the wind, and where the 

 barrier from the sea is at times broken down. At such times the land 

 fauna is either driven away or destroyed, and in the latter instance a 

 "bone bed" is entombed beneath marine deposits which later may come 

 to the light and their territory be again invaded by a land fauna. 



As regards the more ancient sandstone formations, the frequent occur- 

 rence of an abundance of angular feldspar fragments to form an arcose 

 indicates a secular disintegration of granitic rocks under essentially arid 

 conditions. Such an explanation has been applied by Pumpelly* to the 

 Greylock district of Massachusetts, and the writer has found striking 

 illustrations of such deposits from near the Massachusetts-Connecticut 

 interstate boundary. f The recent papers by AYalther,^ Passarge,§ and 

 Davis || indicate that the part the desert has played in geological history is 

 to receive greater attention in the future than it has in the past. 



Acknowledgment 



The writer desires to acknowledge his indebtedness to M. Pelsmacker, 

 the Belgian consul at Granada, who is both a mining engineer and a com- 

 petent geologist, and whose familiarity with the geology of the province 

 has been of great assistance to the writer in his study of the district. 



* R. Pumpelly : Monograph xxi, U. S. Geol. Survey. 

 f Best seen on the summit of Collins hill, near New Milford, Mass. 

 t J. Walther : Das Gesetz der Wiistenhildung. Berlin, 1900. 

 § S. Passarge : Die Kalahari. Berlin, 1904. 



|| W. M. Davis: The geographical cycle in an arid climate. Jour. Geol., vol. xiii, 3 905, 

 pp. 381-407. 



