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Danvarner@aol.com wrote:
> In a message dated 98-07-20 14:24:25 EDT, you write:
> <<  Anybody know whether the typical river/stream bed is soft or firm? >>
>   Growing up on the Mississippi, I'd have to say it's firm and shallow-at
> least in the upper reaches- can't speak for the delta area south of Memphis.

JimC writes:
Growing up on the Mississippi in the delta south of Memphis, I'd have to
say it's firm and shallow for the most part.  The average depth near
Phillips County, Arkansas is about 4' with the very deepest spots
perhaps a hundred feet (very rare and localized due to high velocity
eddies).  Width in this area ranges from about 3/4 mile in the deep
reaches (10'-20' depth) to  about 1.25 miles in the shallow reaches. 
Except where the bank has been artificially stabilized with revetment or
rip-rap, getting in and out would be quite difficult because of the firm
semi-vertical banks.  The nearest bedrock is buried by about a half mile
of alternating sand and clay sediments. 

The southern Mississippi doesn't appear to be all that old in its
present form, having been composed of braided streams until fairly
recently, but the Cretaceous must have similar large rivers, and the
junction of the Mississippi and the Ithabasca in southern Illinois
appears to reflect the northern bifurcation of the Reelfoot rift,
indicating that said junction may have been created by the southern
Illinois inclusion about 1.1 billion years ago.  If any of you are
interested in geology, the inclusion is circular, about 42.5 nautical
miles in diameter, centered at 38 degrees 09 minutes 30 seconds North,
89 degrees 26 minutes 30 seconds West. It shows in water resource maps,
DEM's, gravitational and magnetic anomaly maps, earthquake epicenter
plots, and LandSat and Shuttle images.  I first thought it was an
unrecorded impact crater, but a bolide small enough to generate the
structure wouldn't have had enough energy to create a crater that would
have survived so long. I've enhanced a DEM JPEG of Illinois to increase
vertical color values and bring out the central cone and outer ring if
any of you'd like an off-list image.

> Where there are springs, however, there is the danger of quicksand.
>   To me, the problem with sauropods has always been finding water DEEP enough
> to submerge them ala Burian's famous Brachiosaurus-in-the-fiord painting or
> Knight's early sketch of Cope's Amphicoelias. If these scenes were supposed to
> be occurring in river systems, there must have been a Jurassic Army Corps of
> Engineers around to keep those channels deep enough. 

How true.  You sure won't find deep channels around here, except where
the Corps is actively involved.

> Not to mention lead
> weights around the ankles of those living balloons to keep them submerged. Dan
> Varner.