Februakt 23, 1906.] 



SCIENCE. 



289 



Loup Fork Tertiary of Sioux County, Neb. 

 The skull of this genus, which has been 

 named Syndyoceras, is characterized by 

 two prominent frontal horns which curve 

 inward and by two maxillary horns which 

 rise from a common trunk and curve out- 

 ward. The anterior horns divide the an- 

 terior nares into two parts, the posterior 

 of which resembles a blow hole. The lower 

 canines have become incisiform by migra- 

 tion, and likewise the first premolar has 

 become distinctly caniniform. 



The following abstracts were read by 

 the secretary pro tern, in the absence of 

 the authors of the papers: 



The Eeiveenawan at Lake of the Woods in 



Minnesota: N. H. Winchell. 



A visit in August, 1904, to the south 

 shore of the Lake of the Woods, disclosed 

 large areas of gabbro, apparently identical 

 with that of the Keweenawan seen at 

 Duluth and at other points in northern 

 Minnesota. 



An examination of specimens collected 

 by J. E. Todd for the Minnesota Geological 

 Survey, now in the museum of the Univer- 

 sity of Minnesota, warrants the assumption 

 not only that this rock, under some shades 

 of variation, occurs widely on the south 

 shore of this lake, but also that it is asso- 

 ciated with heavy basaltic rocks quite 

 similar to the black basalts of the Lower 

 Keweenawan, as well as with red granite. 



This discovery, while correcting the prev- 

 alent idea of the 'Laurentian' age of the 

 rocks of the south shore of Lake of the 

 Woods, indicates that the strike of the 

 Keweenawan from Duluth passes north- 

 westwardly, and probably includes the out- 

 crop of copper-bearing amygdaloid lately 

 announced by the Canadian Geological 

 Survey, occurring in the prairie at the 

 north end of Lake Manitoba, where the 

 strike of the formation is northwest and 

 southeast. 



Some Sink-hole Lakes of North Central 



Florida: B. H. Sellaeds. 



The porous and very soluble limestone 

 underlying the Florida peninsula has occa- 

 sioned some unusual topographic features. 

 Owing to the surface mantle of sand, the 

 porous limestone and the general flatness 

 of the country, a very small part only of 

 the rainfall passes ofl: as surface water, 

 the greater part going at once into the 

 ground. The dissolving effect of surface 

 water is shown in the enlargement of 

 stream basins through limestone. The 

 solvent effect of underground water is indi- 

 cated by numerous sink-holes throughout 

 parts of the peninsula. By far the greater 

 number of these sinks are small. Some, 

 however, reach considerable size. All are 

 more or less perfectly circular. In time 

 the banks become less steep through decay 

 of rocks, and the sink thereby enlarged. 

 In limestone regions with little or no clay 

 above, sinks often remain open at the bot- 

 tom, thus forming natural underground 

 entrances for such rivulets or streams as 

 drain to them. In regions holding some 

 clay the sinks are likely to become perma- 

 nently clogged and fill with water, afford- 

 ing a starting point around the sides for the 

 hardwood species of plants. Occasional 

 sink-holes occur of such size as to be entitled 

 to mention as small lakes. Illustration of 

 this kind of lake is taken from a series of 

 sinks on the proposed university grounds 

 at Gainsville. The largest of these spreads 

 over something more than an acre. The 

 banks are thickly clothed with the hard- 

 wood, or 'hammock' types of vegetation, 

 and while steep on one side are sloping on 

 the other. The overflow in the rainy sea- 

 son is carried away by a small stream head- 

 ing near the sink. The sink presents many 

 of the features of a small lake, yet is not 

 so old or so far developed that its sink-hole 

 origin is not clearly evident. Small, cir- 

 cular, possibly solution, lake basins are ex- 



