176 Field Museum of Natural History — Reports, Vol. V. 



these there extends over the lake a fringe of floating bog, composed of 

 a mat of rushes and sedges floating on the lake surface and attached to 

 the shore. Beyond the floating bog, water is shown and on its surface 

 appear representations of aquatic vegetation, such as lilies, bulrushes, 

 etc., which grow in orderly, but sometimes broken sequence from the 

 shore outward. On the bottom of the lake appear masses of water weeds 

 also in zones, each kind of weed contributing its detritus to the masses 

 of calcareous and organic material which slowly fill the lake. The front 

 of the model shows a section of the lake audits adjoining ground. The lake 

 bottom has also been modeled and may be seen through the representation 

 of the lake water. This section shows at the sides and bottom the original 

 gravel and rock basin of the lake. The peat and muck formed from the 

 remains of aquatic vegetation extend towards the center from the sides. 

 The floating bog also appears in section, and the tmderlying peat formed 

 from the vegetable remains dropped from the rush mat is represented. 

 Masses of bladderwort and similar water plants and the peat derived 

 from them are shown in their proper position, as well as the lime- 

 secreting algae and charas growing over the grayish-white marl which 

 they are supposed to have formed on the lake bottom. The model 

 illustrating the relation of soil and rock in glaciated regions is intended 

 to show that in a glacial region the contour of the surface of the soil has 

 no relation to the form of the rock surface below. The model is made 

 of Portland cement laid on expanded metal. It is three feet long, one 

 foot wide, and thirty-two inches high. The scale is 30 feet to the inch. 

 It represents a region such as exists in the agricultural districts south- 

 west of Chicago. The upper surface of the model represents a slightly 

 rolling country with cultivated fields, pastures, farm buildings and a 

 road. The front of the model shows a section through the soil and the 

 rock below. The surface soil is represented lying on a mass of till, which 

 in turn rests upon horizontally bedded limestone. The upper surface 

 of the limestone is represented as having been carved in pre-glacial 

 times to a very rugged topography, but the peaks and valleys of this 

 rock topography are seen to have no bearing whatever on the contour 

 of the gently rolling surface above. In order to bring the peat collections 

 opposite the model illustrating the mode of formation of peat, the table 

 cases in Hall 35 were rearranged, and in the case illustrating the occur- 

 rence of diamond, a new series of minerals and rocks associated with 

 the occurrence of the South African diamonds was installed. In making 

 this installation there was placed in the center of the collection a large 

 label with a cut representing a cross-section of the Kimberley deposit. 

 From appropriate places on this label white silk threads were extended 

 to specimens of the corresponding rocks. Beyond these, specimens of 



