Digging in my yard... what is it?

[Harry Pristis]

16 hours ago, Bev said:

AHarry: "This internal cast is formed within a mold (the clam valves).  The actual  clam valves are the closest we come to an true internal mold.  However, what we typically see are internal casts after the clam valves have long-ago dissolved away.  If the clam valves are intact, their potential to be an internal mold is irrelevant."

 

Clear as mud to me... I have seen external molds of gastropods and have a fair number of them. Nearly all of our Maclurites are internal molds. I make casts using internal and external molds make of plastic from my fossils by filling them with plaster of Paris - that is a cast to me and what the article/link seemed to say also.

 

So, are you saying that the truly scientific correct term for external and internal molds is "external and internal casts"??? Don't use the word mold, substitute it with the word cast and I'll be safe???  This is a lot to wrap my little pea brain around...

I'm sorry I wasn't able to make this clear to you, Bev.  Let's try this:

A mold is a confined empty space.

A cast is the consolidated fill of the empty space.

[Bev]

Harry: "I'm sorry I wasn't able to make this clear to you, Bev.  Let's try this:

A mold is a confined empty space.

A cast is the consolidated fill of the empty space."

 

I think I might get it... There are external molds but NO INTERNAL molds. ONLY internal casts. Right?

[ynot]

By George! I think She's Got it!

[Bev]

1 hour ago, ynot said:

By George! I think She's Got it!

 

Yeah!!! Thank you Harry!  :-D

 

[Wrangellian]

I may regret getting involved in this debate but I see no problem with the term 'internal mould/mold', to me it is less confusing. It makes more sense to me to define all of the matrix inside and outside the shell as the mould, and the (replica of the) shell as the cast. If you wanted to make an accurate replica of a snail or clam shell, including its internal chamber, you would have to make an internal part of that mould as well as the external part (and in a snail in particular these would be contiguous), and that's what nature does. It's simpler than saying you're "using a mould and a cast to make a cast"!

If for some reason the casting material that ends up filling the mould is so similar to the internal mould's material that it is poorly differentiated and inseparable from it, then the whole thing could be described as a cast. I also have no trouble with the term steinkern, and I will use it if I wasn't to avoid a debate with someone... if they already know the term! But if you are going to use the term 'cast' for a steinkern, please specify 'internal' or 'living chamber' or something like that, just as I would specify 'internal' mold. 'Endocast' is fine, I guess. Just not 'cast'.

http://paleo.cortland.edu/tutorial/Taphonomy%26Pres/preservation.htm

[Harry Pristis]

You can find just about anything on the internet.  The footnote below the chart "after Roberts" sums it up:  * Note that molds are produced directly as imprints of the shell and casts are produced from molds.

What this author doesn't acknowledge is that steinkerns (internal casts) are formed while the shell (our example) is still intact -- they are direct imprints of the shell.  The interior of the shell is the mold.  This author (and Roberts, by implication) seems to be saying is that there is some extra step -- a cast of the shell formed -- to produce an "internal mold."  Nonsense.

[Al Dente]

I'm not sure which term would be most technically correct but if you do a Google Scholar search of published reports you can find how frequently these terms are used. Internal mold is more commonly used than internal cast. Steinkern is the most popular used.

 

 

[Harry Pristis]

   Professional paleontologists, those who write technical papers, are not necessarily well-versed in language skills.  And, this "internal mold" thing is the sort of mis-use of language that a journal editor may ignore if the meaning is clear or the reference is inconsequential.  A similar example is "scute" which is slipping into some papers as a substitution for "osteoderm" despite the difference between the two body parts.

 

   Still, language is dynamic.  New words are coined, meanings are corrupted, new usages are offered, and any of these offerings may be picked up by successive workers.  Most of the resulting changes to the science vocabulary and usage are good things, providing narrower definition and specificity.  But, some are just sloppy, a poor reflection on the language skills of whomever first mis-used the terms.

 

   Yet, the nature of scientific writing is much more constraining on mis-use of language than informal writing or conversation.  How often have we heard a news commentator or reporter say, "It begs the question . . ." trying to suggest that "It invites the question . . ."  when the true, historical meaning of "to beg a question" is actually "to ignore a question."

[Plax]

"deja vu all over again!" (have forgotten whom I'm quoting) I'm with you Harry. I like logical speech. This discussion was beat to death a while back.

[Wrangellian]

So only you guys are using logic and sense when you speak and I'm just mindlessly parroting things I've heard other people say? WRONG!

My definitions might be slightly different than yours, but this usage makes sense to me and a lot of people.

OK, so when does the matrix that surrounds this bivalve go from being a mould to a cast?

[ynot]

10 minutes ago, Wrangellian said:

So only you guys are using logic and sense when you speak and I'm just mindlessly parroting things I've heard other people say

I never said anything like that, so I guess I am not one of "You guys".

 

11 minutes ago, Wrangellian said:

so when does the matrix that surrounds this bivalve go from being a mould to a cast?

Never, it is always a mould. I think the best way to describe it would be to call it "A mould of the interior of a shell". (But I guess that is not much different than calling it an internal mould.)

 

Now I am all confused!

Tony

[Bev]

WOW, my poor little pea brain is swirling! I just want to do what is right and what the majority of non-fossil addicts will understand...

[Wrangellian]

That's what I'm trying to do, too Bev. I'm afraid that calling an internal mould a 'cast' will lead beginners to think they have a cast of the body (shell) when all they have is the internal mould which is the matrix that filled the living chamber (an impression of the interior surface.)

I wish I had thought of this specimen earlier...

Harry et al would call the internal part on the left a 'cast' or 'endocast':

 

But look! It is contiguous with the outer matrix, because the valves were open partway when it was buried:

 

I could reunite the two halves and pour something in the narrow gap where the shell used to be to make a cast of the shell: (I can't quite get the two pieces together without forcing them)

 Then I would break them apart and have a replica of the shell. To me that would be the cast, and everything around it is (was) the mould. I have seen it done wonderfully with larger examples of these Trigonias.

This is not sloppy, it seems pretty coherent to me.

 

Here is another one I could possibly do, though the gap is so narrow that whatever matrix you poured in might not fill every nook and cranny, but Nature could do it under the right conditions.

[Plax]

14 hours ago, Wrangellian said:

So only you guys are using logic and sense when you speak and I'm just mindlessly parroting things I've heard other people say? WRONG!

My definitions might be slightly different than yours, but this usage makes sense to me and a lot of people.

OK, so when does the matrix that surrounds this bivalve go from being a mould to a cast?

no insult intended Wrangellian. Your definition is as correct as anyones's. Molding and casting are different when used as verbs or when used as nouns such as cast and mold. Certainly sediment is "cast" from the mold of the shell whether it is internal or external. Once the shell is gone the sediment would be used as a mold to make a cast of the shell. The current literature is dominated by "mold" usage (per Aldente's research) for the sediment and I personally don't care what anyone uses as long as I understand what the writer is saying.

[ynot]

11 minutes ago, Plax said:

don't care what anyone uses as long as I understand what the writer is saying.

Hear, hear! Or os it Here, here!

Either way-- I could not have said it better.

Tony

[Bev]

1 hour ago, Plax said:

 I personally don't care what anyone uses as long as I understand what the writer is saying.

 

Yeah! I could be wrong, but I think if this were a paleontologists only forum picking at the details of how something is said would be appropriate. That it is a general fossil enthusiasts forum with a direction of being correct in all aspects of whatever applies to fossils makes it a little different. That said, my identification of these internal casts has now change to perhaps a more correct term. Thank you all for your input.  :-)

[Wrangellian]

Agreed. Use whatever term you want as long as you're careful to make it clear to the listener/reader what you mean by it. There may be no ideal concept when you have only vague or simplistic terms to work with, but that's what makes language fun - when you start having to adapt these terms to something like this. Who came up with 'Internet', anyway?