tjti Field Ml-seim or Natceal Histoey — Repoets, Vol. V. 



t. 1 '■ •*-.:«• ixlc-:;!, <.vrr l! ' ' a frinjjc of fl-.i'.- • .; ' >1 "1 



a tnal "t rvi h.--  an<l ' .. sti.::;' <i'A the lake viil.i. «. 4tu<i alUkviicU lo 



*'■■ shore. M' • ' .ri'.'l • ^'.r i^ sh <wa and on its surface 



- ar n: >rt ri, : ui h as lilies, btilrushes, 



'. ^r<)\v in orderly, but wimelimes hmken sctjucncc from the 



retmtward. On the bottom of the lake appear ina-sscs of water weedf 



' in zones, each kind of weed contributing its detritus to the nmsMt 



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



ofUiemo«! " " lof the lake and i* ^lund. The lake 



' •" ' ha->ai-ui>i.vn III' 1 andmaylxjsc' . uc representation 



ikcwatcr. This.-.  I. ■;» showsat the . .>ottomtheorifnnal 



' i:.il rock l>asin of the lake. The jx»t and muck formed from the 

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

 The floating Ikjr also appears in section, and the underlying peat formed 

 from the vc>:eLaV)le remains dropped from the rush mat is repr es en ted. 

 Masses of bladdcrwort and similar water plants and the peat derived 

 from them arc sht)wn in their proper position, as well as the lime- 

 -^tTctinR algae and charas growing over the graNnsh-white marl which 

 th« y arc supjxjsed to have formed on the lake bottom. The model 

 jlhislrating 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, ooe 

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

 It represents a rej^on such as exists in the agricultural districts south- 

 west of Chicago. The up|x*r surface of the model represents a slightly 

 country with cultivated fields, pastures, farm buildings and a 

 r ->aa. The front of the mtxlel shows a section through the soil and the 

 rock below. The surface soil is rer '■•■ "ted lying on a mass of till, which 

 in turn rests u{X)n horizontally I . - . i limestone. The upper surface 

 of the limestone is represented as having been car\'ed in pre-glacial 

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

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

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

 "c the model illustrating the mode of formation of peat, the table 

 t .1 * ;n Hal! ^5 were rearranged, and in the case illustr.T he occur- 

 rcncx* ol diamond, a new series of minerals and rocks a >- « alcd with 



fVo r- . ,,rr. ^ flip South African diamonds was install-' Tn making 



re was placed in the center of the o 1 a large 



label wi»h ft cut representing a cross-section of the Kimbcrley deposit. 

 Prom riatc places on this lalxJ white silk threads were extended 



lo spc' of the corresponding rocks. Beyond these, specimens of 



