[Bass]

As near as I can tell from the geologic map of the US there are mostly sedimentary rocks in Cedar County. (The Iowa Geologic Survey is too cheap to put a geologic map on its site.) BUT, the occurrence of galena, a crystalline mineral, is evidence of intense mineralization in the area of eastern Iowa.  

So there is magma under them there plains.

AAHHHH, Jimmy, Jimmy Jimmy.  And this from a decrepit old oiler like yourself as well!  Stand up for your profession, you big softy.

(and I bet you made that magma comment just for me)

The galena deposits JimBob refers to (actually they're lead-zinc deposits) are known as Mississippi Valley Type (MVT) deposits and (unbelievably) are common in Iowa and Illinois along the Mississippi River. 

This particular class of ore deposit is low temperature-low pressure hosted by particular types of carbonates (sedimentary rocks)- and is almost always associated with hydrocarbons.  It is thought that the lead, zinc and sulfur were derived from basinal brines near reef facies.  These mineral-rich brines may have formed during conversion of organic material to hydrocarbon.  The brines migrate outward into permeable carbonate sequences (karst, reef facies); deposits almost always occur in areas of high dolomitization.

One of the few metallic mineral deposits that are probably not related to magmatic activity.  

[JimBob]

SEE?

I SAID hot water!

('hydros' in the Greek meaning water and 'thermos' meaning heat.)

Hydrothermal or other vados water activity produced these. They are crystals deposited on and in the host rocks - shale or black limestone in the last three picture.

And as for oil bearing strata - EVERYONE knows black shale or limestone means they are very high in organic content! D'Oh!

(... magma is EVERYWHER!)

[Boone (OP)]

Thanks for the all the info so far. Boone

[Geezer]

EVERYONE knows black shale or limestone means they are very high in organic content! D'Oh!

Yup! Even I knew that.

[JimBob]

EVERYONE knows black shale or limestone means they are very high in organic content! D'Oh!

Yup! Even I knew that.

Thank You, Thank you Verry much