INTRODUCTION.  15 
setts  and  Connecticut,  A.  C.  Spencer  for  southeastern  New  York  and 
New  Jersey,  G.  B.  Richardson  for  Texas,  Samuel  Weidman  for  cen- 
tral Wisconsin,  Alfred  H.  Brooks  for  Alaska,  John  A.  Dresser  for 
the  Eastern  Townships,  G.  F.  Matthew  for  New  Brunswick,  and 
Bailey  Willis  and  Eliot  Blackwelder  for  China.  Our  thanks  are 
especially  due  to  Mr.  Ezequiel  Ordonez  for  an  excellent  and  compre- 
hensive summary  of  the  pre-Cambrian  geology  of  Mexico.  Finally 
we  would  acknowledge  our  indebtedness  for  valuable  criticism  to 
Messrs.  Frank  D.  Adams  for  criticism  of  the  section  referring  to  the 
original  Laurentian  and  Hastings  districts,  E.  R.  Faribault  for  south- 
ern Nova  Scotia,  Robert  Bell  and  other  members  of  the  Canadian 
Survey  for  the  northern  interior  of  Canada,  J.  M.  Boutwell  for  Utah, 
N.  H.  Darton  and  F.  C.  Calkins  for  Idaho  and  Montana,  J.  A.  Taff 
for  Indian  Territory,  Oklahoma,  and  Texas,  F.  L.  Ransome  for  Ari- 
zona and  Idaho,  Waldemar  Lindgren  for  New  Mexico,  and  to  others. 
