Description:
	     data set on heavy metals in the topsoil of an area of about
	     3~km$^2$ that borders a river.

The data set contains the following variables:

 - x,y :    geographical coordinates of locations where soil was sampled,
 - zinc, cadimum : heavy metal concentration in the soil samples in
	    mg metal/kg of dry soil
 - ffreq : an integer variable that codes how frequently a location is
	    flooded by the river
 - lime :   a factor with levels 'yes' or 'no' coding the
   	    presence of calcium carbonate in the soil samples.

In R:

  d.hm <- read.table("ftp://stat.ethz.ch/Teaching/Datasets/hm.dat",
		     header=TRUE)

> with(d.hm, table(lime, ffreq))
     ffreq
lime   1  2  3
  no  46 42 23
  yes 35  6  0

> str(d.hm)
'data.frame':	155 obs. of  6 variables:
 $ x      : int  181072 181025 181165 181298 181307 181390 181165 181027 181060 181232 ...
 $ y      : int  333611 333558 333537 333484 333330 333260 333370 333363 333231 333168 ...
 $ cadmium: num  11.7 8.6 6.5 2.6 2.8 3 3.2 2.8 2.4 1.6 ...
 $ zinc   : int  1022 1141 640 257 269 NA 346 406 347 183 ...
 $ ffreq  : int  1 1 1 1 1 1 1 1 1 1 ...
 $ lime   : Factor w/ 2 levels "no","yes": 2 2 2 1 1 1 1 1 1 1 ...

Source: Andreas Papritz, D-UWIS, ETH Zurich