630 PRINCIPLES OF STRATIGRAPHY 



from Miocenic to the present. Its material is derived from the crys- 

 talHnes of the Sierra Nevada, from the northern flanks of which it 

 extends for twenty-five miles, and locally from the Triassic dolo- 

 mite of the Sierra Harafia (Alhambra formation). The formation, 

 approaching a thousand feet in thickness, is a conglomerate near 

 the mountains with pebbles varying "from a fraction of an inch to 

 six inches or more in length." Within the various stream valleys 

 local peculiarities of rock material exist, corresponding to the pecu- 

 liarities of the rocks in the respective headwater branches of 

 these streams. At a distance from the mountains fine material 

 prevails, much of it of a loess-like character, indicating wind and 

 playa-lake deposition. Floated plant material, such as roots and 

 brushes, appear to be characteristic of some of the finer deposits. 

 These torrential deposits seem to be intimately related to the 

 semiarid conditions of the interior of Spain, caused by the monsoon 

 winds. These winds blow northward from the Mediterranean in 

 summer, crossing the Sierra Nevada and leaving much of their 

 moisture on the southern slopes. Descending the northern slopes 

 they are relatively drying winds and so permit the formation of 

 these periodic torrential deposits. 



Similar torrential deposits of great thickness and ranging in 

 age from late Tertiary to the present are described from southern 

 Italy (31 •.2go) . A marked cross-bedding structure, already re- 

 ferred to (Fig. 123), so similar to what is commonly found in an- 

 cient sandstones, is characteristic of many of these deposits. The 

 Siwalik formation of India has already been cited as a subaerial 

 deposit of similar character and age. It is of great interest in that 

 it reaches the enormous thickness of 15,000 feet. Here also belongs 

 in part the Mollasse of the Alps. This is a complex series of 

 light-colored sandstones and conglomerates with occasional lime- 

 stones, found in the Alpine forelands, in the south of Germany and 

 in Switzerland. The lower part of the Mollasse is of Oligocenic age 

 and begins as a marine series. In southern Germany this reaches in 

 places a thickness of 600 meters (Bavaria) and is followed by an 

 immense series of fresh water sands and conglomerates approach- 

 ing a thousand meters in thickness. This series shows in part 

 brackish water and in part fluviatile and lacustrine conditions. The 

 brackish water phase contains Cyrena, Cerithium, Cytherea, etc., 

 and the fresh water Limnseus, etc. Numerous leaves and other 

 remains of land plants (Cinnamomum, Juglans, Ouercus, Betula, 

 Rhamnus, etc.) are found locally, forming what is known as 

 "Blattermollasse" and forming occasional beds of brown coal, 

 which is extensively exploited in the Bavarian fore-Alps. Red sedi- 



