AutoRanging Resistance Sensor

I am a digital person and know enough Analog to be dangerous. I have a requirement for a wood moisture sensor. The resistance values range from 100k to 100m. I've enclosed a sketch of a digital solution. It involves a mux with different R values being driven by a constant current source. I would keep switching in different R values until I got a reading on the ADC then multiply the reading by the selected R value to get the final resistance. It will work but it seems a little kludgy to me. Can any of you hot shot analog wizards out come up with an auto ranging solution using op-amps or ???

Any help will be greatly appreciated.

Erm, can't figure that circuit at all - whats the amp on the left doing?

How about feeding a constant voltage to the sample and using a diode as a logarithmic converter (plus a second calibration diode to deal with temperature change)? You'll need very high impedance opamp to amplify the output at those impedances (CMOS or JFET input opamp in non-inverting configuration).

That op-amp looking thing is a 10 bit ADC. Probably picked the wrong symbol.

Ah, wrong shape, wrong direction (signals go from left to right if possible, otherwise arrows are needed). Triangle is amplifier or buffer.