304 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



courses, to present perpendicular cliffs. Vertical tubes pen- 

 etrate this deposit throughout, which apparently result from 

 the decay of grass and roots. In addition to these, the re- 

 mains of plants, land-snails, and the bones of terrestrial mam- 

 mals occur in it. The thickness of this deposit is very great, 

 being often 1000, and in some cases even 2000 feet. 



Various theories have been proposed to account for this 

 remarkable formation. Kingsmili regarded it as a deposit 

 during a period of marine submergence; while Pumpelly, 

 from his studies of parts of the region, supposed it to have 

 been accumulated in a great inland lake, which received the 

 drainage of a vast area. Belt imagined such a lake to have 

 been formed by the damming-up of the rivers by an enor- 

 mous glacier tilling the North Pacific, applying a similar 

 hypothesis to the loess of the Rhine (Record for IS 7 7, p. 

 ISO). According to Von Richthofen, while it is true that 

 certain limited areas of the loess are, as supposed by Pum- 

 pelly, deposits from water, and thinly laminated, these are 

 distinct from the great mass of unlaminated loess which 

 overlies them. This he supposes to be a sub-aerial forma- 

 tion due to the transport of dust by the winds, to which, in 

 the vicinity of the hills, rain and small streams have con- 

 tributed by bringing down coarser material. Such agencies, 

 operating through long ages in an interior basin, in which, 

 by reason of a small rainfall, there is is no outflow of waters, 

 must result in an accumulation of material not unlike the 

 loess of China, as described by Von Richthofen. 



FOSSIL SPONGES. 



S. J. Wallace has examined the geodes found in the Keo- 

 kuk (Lower Carboniferous) limestone over a great area in 

 the Upper Mississippi valley. They are shells of chalcedonic 

 silica of from a few lines to two feet in diameter, sometimes 

 empty, but at other times tilled with agate, crystalline 

 quartz, or calcite, and have long been suspected to be organ- 

 ic in origin. Wallace has confirmed this view, and shown 

 them to be casts left by the decay of sponges, of which they 

 often bear the outward markings. lie lias described several 

 species which he refers to a new genus, Biopalla. These 

 sponges are seen to have grown in some cases over and 

 around projecting masses of rock, and, in one case, within a 



