226         CONTRIBUTIONS   TO    ECONOMIC   GEOLOGY,  L906,  PART    I. 
MAPS  AND   OTHER   PUBLICATIONS. 
Dubuque,  Iowa,  is  on  the  south  edge  of  the  Lancaster  quadrangle, 
which  extends  northward  about  35  miles  from  latitude  1_'  :>()'. 
East  and  west  of  Dubuque  the  quadrangle  extends,  respectively,  <) 
and  17  miles.  The  United  States  Geological  Survey  has  issued  topo- 
graphic and  geologic  maps  of  this  quadrangle  which  are  together 
available  in  the  geologic  folio  of  the  Lancaster-Mineral  Point  area 
(folio  No.  145, Geologic  Atlas  U.S.,  price  25  cents).  The  topographic 
maps  are  also  issued  separately  and  sold  for  5  cents  each.  Other 
useful  maps  and  discussions  of  the  geology  of  the  district  have  been 
issued  by  the  State  surveys,  as  follows: 
Calvin,  Sami  el,  and  Bain,  II.  F.     Geology  of  Dubuque  County:   [owa  Geol.  Survey, 
vol.  10.  L900,  pp.  379  622. 
Beyer,  S.  \Y.     Supplementary   reporl  on  Portland  cemenl  materials  in  [owa:   Bull. 
[owa  Geol.  Survey  No.  3,  1906,  36  pp. 
Grant,  U.  S.     Reporl  on  the  lead  and  zinc  deposits  of  southwestern  Wisconsin,  with 
alias:  Bull.  Wisconsin  Geol.  and  Nat.  Hist.  Survey  No.  I  I.  [906,  !<><>  pp. 
AGE  AND   DISTRIBUTION   OF   THE   ROCKS. 
The  principal  rocks  exposed  along  Mississippi  River  and  near  the 
months  of  its  tributaries  between  Dubuque,  [owa,  and  Cassville, 
Wis.,  together  with  their  ages  and  essential  features,  are  comprised 
in  the  following  table: 
Rocks  i  tposed  north  of  Dubuque,  Towa. 
A  few  miles  hack  from  the  river  the  Maquoketa  shale  and  Niagara 
limestone  are  present  in  the  section,  above  the  Galena,  but  these 
rocks  have  no  bearing  on  the  present  subject.  The  beds  of  particular 
importance  are  the  limestone  and  shale  of  the  Platteville,  the  basal 
Galena  beds,  and  the  residual  clay  and  loess,  all  of  which  are  exposed 
in  the  bluffs  of  the  Mississippi  River  gorge  between  Dubuque  and 
Cassville. 
MANUFACTURING    SITES. 
Along  the  greater  part  of  the  river  front  between  these  cities  the 
bluffs  rise  steeply  to  a  height  of  60  to  100  feet  above  the  flood  plain  and 
then  slope  more  gently  to  a  total  height  of  150  to  200  feet  above  the 
river.     On  both  sides  of  the  river  a  railroad  runs  close  to  the  base  of 
