# Geology question **URL:** \ **Category:** Factual Questions\ **Created:** [April 29, 2014, 3:05am UTC](https://boards.straightdope.com/t/geology-question/687247 "2014-04-29T03:05:55Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [May 3, 2014, 1:41pm UTC](https://boards.straightdope.com/t/geology-question/687247/21 "2014-05-03T13:41:37Z")
(I shouldn’t have used the word “micro-plate” in my original post. “Terrane,” “micro-terrane,” or (for the bigger ones) “block” is more correct.) ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [May 4, 2014, 12:01am UTC](https://boards.straightdope.com/t/geology-question/687247/22 "2014-05-04T00:01:24Z")
The way exotic terranes are traded off between continental plates is one of the most fascinating topics in plate tectonics for me. When I concurred completely with your post 2, I understood you were guessing “perhaps limestones” and referring non-specifically to metamorphism by saying “say, shales.” I didn’t take it as you were saying shales are metamorphosed from limestone, you obviously know better than that, you were just alluding offhand to sedimentary metamorphism in general, so I still think your original guess off of just the photographs was informed and astute. ---
**Author:** ![user\_hostile](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/user_hostile/32/474_2.png) [@user\_hostile](https://boards.straightdope.com/u/user_hostile)\ **Post date:** [May 4, 2014, 1:07am UTC](https://boards.straightdope.com/t/geology-question/687247/23 "2014-05-04T01:07:09Z")
> [@MrDibble](#): > > Yeah, I know, but the rocks in question are not Monterey, they’re Franciscan. I know this because I can [read a geological map](http://www.quake.ca.gov/gmaps/GAM/sanluisobispo/sanluisobispo.html). All the actual beach deposits at the Point are keyed as _KJf_ - that’s Franciscan sediments. > > I wasn’t saying they’re Franciscan _because_ they’re siliceous, I was saying they’re likely that _particular combo_ of siliceous _because_ they’re Franciscan _and_ they don’t _look_ like the other characteristic Franciscan rocks (Ophiolites aren’t sedimentary and are keyed _KJfv_ anyway, serpentinites look nothing like that and would be _KJfv_ too, limestone _would_ be _KJf_ but (especially in a well-watered area) would be all pitted even if interbedded like that, which I’ve never seen anywhere else, etc) Sorry, I was in a hurry with my rather terse response (wasn’t trying to be snippy). The link you provided states the date as 1958. The link I provided is from 1976 (and I found a nice refined version in living color [from 1979](http://ngmdb.usgs.gov/Prodesc/proddesc_290.htm)). You’ll note the _Kjf_ formations surrounding San Simeon were reassigned to the _Tm_ in the later versions. Also, note the geological cross-section (B-B’) in the upper-right-hand corner of sheet 1. The line saunters right on by San Simeon point. There is another point up the coast that is surrounded by _Kjfmv_. That would be Piedras Biancas Point. A great resource are these two links [The National Geologic Map Database](http://ngmdb.usgs.gov/ngmdb/ngmdb_home.html) and the [USGS Publications Warehouse](http://pubs.er.usgs.gov/). ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [May 4, 2014, 1:25am UTC](https://boards.straightdope.com/t/geology-question/687247/24 "2014-05-04T01:25:37Z")
> [@Johanna](#): > > The way exotic terranes are traded off between continental plates is one of the most fascinating topics in plate tectonics for me. > > When I concurred completely with your post 2, I understood you were guessing “perhaps limestones” and referring non-specifically to metamorphism by saying “say, shales.” I didn’t take it as you were saying shales are metamorphosed from limestone, you obviously know better than that, you were just alluding offhand to sedimentary metamorphism in general, so I still think your original guess off of just the photographs was informed and astute. Thanks for your confidence in what I’d meant by that! You’re right, I should have been clearer in my phrasing – but I didn’t really mind njtt’s clarification. ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [May 4, 2014, 1:33am UTC](https://boards.straightdope.com/t/geology-question/687247/25 "2014-05-04T01:33:16Z")
To clarify further: I was taught that shale generally metamorphizes into slate, while limestone generally metamorphizes into marble. I’m sure there are all sorts of alternate pathways, but I presume these are still considered typical ones. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [May 4, 2014, 9:35am UTC](https://boards.straightdope.com/t/geology-question/687247/26 "2014-05-04T09:35:41Z")
> [@user\_hostile](#): > > Sorry, I was in a hurry with my rather terse response (wasn’t trying to be snippy). > > The link you provided states the date as 1958. The link I provided is from 1976 (and I found a nice refined version in living color [from 1979](http://ngmdb.usgs.gov/Prodesc/proddesc_290.htm)). > > You’ll note the _Kjf_ formations surrounding San Simeon were reassigned to the _Tm_ in the later versions. Ooh, thanks , I stand corrected. CalGeo needs to update their online maps 🙂 Monterey it is. I think the lithology I mentioned would still be the same, though - chert-shale-sand interbedding? ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [May 4, 2014, 1:41pm UTC](https://boards.straightdope.com/t/geology-question/687247/27 "2014-05-04T13:41:57Z")
> [@MrDibble](#): > > Ooh, thanks , I stand corrected. CalGeo needs to update their online maps 🙂 Monterey it is. I think the lithology I mentioned would still be the same, though - chert-shale-sand interbedding? Of those three, it looks like most of what’s in the OP’s photos is chert. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [May 4, 2014, 5:44pm UTC](https://boards.straightdope.com/t/geology-question/687247/28 "2014-05-04T17:44:44Z")
> [@JKellyMap](#): > > Of those three, it looks like most of what’s in the OP’s photos is chert. It’s really, _really_ hard to say without being there. I’d need to see a hand specimen to be sure. ---
**Author:** ![jimbuff314](https://avatars.discourse-cdn.com/v4/letter/j/c57346/32.png) [@jimbuff314](https://boards.straightdope.com/u/jimbuff314)\ **Post date:** [May 4, 2014, 7:22pm UTC](https://boards.straightdope.com/t/geology-question/687247/29 "2014-05-04T19:22:20Z")
I agree that those photos do not have nearly a high-enough resolution to identify chert. However, from the Wiki on [chert](http://en.wikipedia.org/wiki/Chert) : “Diatomaceous chert consists of beds and lenses of diatomite which were converted during diagenesis into dense, hard chert. Beds of marine diatomaceous chert comprising strata several hundred meters thick have been reported from sedimentary sequences such as the Miocene Monterey Formation of California and occur in rocks as old as the Cretaceous.” Posted by someone who lives near and has spent time in the areas of the _novaculite_ variety of chert in the Ouachita Mts of eastern OK, western AR - rather well-known to flint-knappers. [Previous page](https://boards.straightdope.com/t/geology-question/687247.md?page=1)