Wednesday, February 1, 2012

Ordovician Limestone ~ Waiting for Castiglione

Giovanni Benedetto Castiglione (1609 – 1664) was one of the Baroque’s preeminent artists.  His drawings, etchings, and paintings reflect the masters he studied and learned from, artists such as Rubens and Rembrandt.  Yet his works are exquisitely his own, as the new exhibit (The Baroque Genius of Giovanni Benedetto Castiglione) at the National Gallery of Art in Washington, D.C. makes abundantly clear.  Indeed, the exhibit’s materials describe his etchings as “the most distinctive of any Italian artist of the period.”  In turn, Castiglione influenced a subsequent generation of artists including members of the Tiepolo family of Venice, among others.

I didn’t know I’d been waiting for this exhibit, but I had, ever since I acquired a small slab of Ordovician limestone.  A singular aspect of much of Castiglione’s work offers the connection to my piece of fossil-bejeweled rock.  At least it does in my eyes.

The National Gallery of Art’s exhibit takes a fascinating approach to its display of this selection of Castiglione’s drawings and etchings, hanging them next to works by the artists who influenced him, those who taught him, those he explored.  But even more than that, this exhibit presents us with works by the artists who felt his influence.  There, side by side by side, one can discern that which sets much of what Castiglione drew and etched apart from the works of those who preceded him and those who followed him.  As I walked the gallery rooms of the exhibit, I often could tell from a distance which were Castiglione’s pieces.  They have an energetic density.

A couple of examples may suffice to show this aspect of his work.  (These images are from Wikimedia Commons and are in the public domain.)  Castiglione’s etching of Circe Changing Ulysses’ Men into Beasts, a work from late in life, allows a white space to encircle Circe, but it’s a dynamic space, being intruded upon by branches and a hanging cloth, and the shadows appear ready to overtake it.  The remainder of the paper is densely populated.  Details abound.

In Noah Leading the Animals into the Ark, executed in brush and oil paint, there is action everywhere, even in the sky.  Castiglione blurred and blended foreground, middle ground, and background, giving us no empty space between each.

Of this latter work, Anne Midgette, who reviewed the exhibit for the Washington Post, (January 30, 2012), observes
[It is a] lyrical image of Noah leading the animals onto the Ark, every corner of the paper crackling with activity as the animals curl in a kind of wave toward the gangplank, guided by Noah’s pointing arm.
Indeed, she identifies this as one of the main aspects of this collection of Castiglione’s work.
But he was never careless in his use of paper. There is very little white space, or down time, in Castiglione’s works here; they are all-over compositions, filling every square inch of the surface, art actively happening everywhere you look.
As for my slab of Ordovician limestone?

This little chunk of rock, six inches long on the diagonal from lower left corner to upper right, has sat on my desk for a couple of weeks and for that time I’ve wondered how best to describe it.

Now and then I’ve taken a jeweler’s loupe and lost myself in a visual tour of its many mysteries.  The sheer abundance of the fossils on this rock is staggering.  This fossil-filled rock captures some of the sheer exuberance of the Ordovician ocean that covered Indiana some 470 to 444 million year ago.  According to paleontologist Lynne Clos, “The greatest diversification in the history of animal life took place during the Ordovician.”  (North America Through Time:  A Paleontological History of Our Continent, 2008, p. 37.)

Provenance of this rock?  It’s an acquisition, not a find, coming with a label identifying it as from the Brookville Formation in Indiana.  As I soon learned, this follows the local designations advocated by the late Helen Hay, who was a geologist at Earlham College.  (Helen Hay and Jon Branstrator, Guide to Field Trips, National Association of Geology Teachers, East – Central Section, September 23-24, 1989.)  The formal name recognized by the Indiana Geological Survey and the U.S. Geological Survey is the Dillsboro Formation which applies to several of the formations identified by Hay, all of them Upper Ordovician.

The most obvious of the fossils embedded in the limestone are the shells of brachiopods, bivalved marine invertebrates which flourished during the Ordovician.  Each of their valves or shells has equilateral symmetry (divisible into two equal pieces), but each creature’s two shells (top and bottom valves) are dissimilar.  Most of those on the rock appear to be of the genus Strophomena.  The picture below shows a close-up view of the interior of a ventral shell from what is perhaps S. planumbona.  Overlapping it on the upper left is, I believe, the exterior of a dorsal shell from the same species.  Characteristically, the exterior dorsal shell of this species is prominently convex toward the outer (curved) edge.

But as one’s perspective dissolves from the long shot to the medium shot and then to the close-up more, much more, comes into view.  We are drawn into a new world of myriad fossils and fragments of fossils.  It’s a phenomenon of fossiliferous limestone.  Nearly everywhere one turns there’s something different to explore.  From the previous picture, we pan up right and several pocked stalks of bryozoans come into view.  These are the calcareous structures the minute colonial invertebrates built and left behind.  Genus and species?  Beyond my ken.

We zoom in even closer and the fossilized remains of sea lilies or crinoids appear.  All we have on this rock are small, perforated disks.  These are the complex invertebrate’s columnals, the skeletal ossicles that covered the stem anchoring the animal in place.  With this close-up view, the wonderful variety of the ossicles emerges, from squared outlines to "five-dimpled" interiors (you'll see what I mean by the latter).  Once again, as we come ever closer, any ability to identify what emerges abandons me.  A extensive, detailed guide just to the shape and patterns of the columnal ossicles would be grand, but, alas, . . . I have to assume identification of genus and species cannot be based on those alone.  [Later note:  But see comment and response below.]

Although I have drawn on the movies for this tour (long shot, pan, . . .), I now think my journey through the Castiglione exhibit offers me the perfect simile for this fossil-filled limestone.
It is like a Castiglione etching, filled with energetic density.


  1. Apparently crinoid genera often can be determined based on columnar shape. I'm pretty sure the columnal at the center of your last picture is Cincinnaticrinus. It looks like there are some gastropods in there, as well.

  2. Alton:

    Thanks so much for the comment. You were absolutely right about the use of columnals in identification of crinoids. With more deliberate searching on the web, I found a number of sites that use the shape of columnals as part of the identification process. The material posted by the Dry Dredgers, an association of amateur geologists and fossil collectors out of Cincinnati, Ohio, is very useful (

    Cincinnaticrinus looks correct for the columnal in the last picture. Although I spot what might be gastropods in that picture, at least one (under some greater magnification) looks like a columnal on edge. Not sure about the others. Based on the Dry Dredgers material, the crinoid whose square columnal appears in the second to the last picture may be of the genus Xenocrinus.

    I've also continued exploring the literature on Indiana bryozoans and the little stalks shown in one of these pictures may be from the bryozoan genus Hallopora. And, if that's correct, rather than being "pock marked," they feature little knobs called monticules.

    All in all, a healthy reminder to me that I need to avoid the cardinal paleontological sin of throwing up my hands and saying something's too tough to identify. With enough work and help (!!), at least something is likely to be worked out.



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