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Kamnolom mlinskih kamnov / Millstones quarry EarthCache

Hidden : 04/22/2014
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3.5 out of 5

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Geocache Description:

(SI) Lepo ohranjen kamnolom z jasnimi krožnimi izseki na mestu odstranjevanja materiala za mlinske kamne. Izjemna kulturna dediščina!

Prosimo, preberite opis tega geološkega zaklada in si zapišite naloge za vpis še pred odhodom na teren! NE POŠKODUJTE STEN KAMNOLOMA!

1. Kamnina iz katere so bili mlinski kamni iz tega kamnoloma je kremenov konglomerat. Oglejte si kamnino ob vznožju stene in na številnih okruških okoli nje. Kako velika so »zrna« kremena v kamnini?
2. Izberite enega od kosov konglomeratnega kamna, ki ležijo na tleh - naj bo čim bolj kompakten, nerazpokan. Poskusite ga odlomiti ali zdrobiti s kladivom (ali drugim kamnom). Pazite da pri tem ne poškodujete sebe ali koga v svoji bližini.
2.a: Ali je kamen mehak? Ga je lahko zlomiti?
2.b: Kaj mislite da je bil glavni izdelek tega kamnoloma: Beli ali črni mlinski kamni? Ugotovitve iz prejšnje naloge (2.a) vam lahko pomagajo pri odgovoru.
3. Stena kamnoloma ni enotne barve. Kakšni odtenki prevladujejo? Kaj je po vašem mnenju vzrok za takšno obarvanost?
4. NEOBVEZNO: Poiščite še eno zanimivost: Nekje na stenah kamnoloma se nahaja »osnutek« mlinskega kamna, ki ga niso do konca izsekali iz skalne stene. V pomoč vam bo njegova slika v spodnjem opisu (slika 3), ter na informacijski tabli na koordinatah Geološkega zaklada.
4.a: V katerem delu kamnoloma se nahaja nedokončan mlinski kamen? Ko ga najdete, si zabeležite koordinate.
4.b: Izmerite višino od tal do spodnjega roba nedokončanega kamna.
4.c: Izmerite razdaljo od kamna do koordinat Geološkega zaklada (info table).

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(ENG) Well preserved millstones quarry, with clearly visible rounded hollows where material for millstones has been quarried. An unique cultural heritage!

Please, read the description of this EarthCache and write down logging tasks before visiting it in the nature!

1. Millstones have been cut out of the rock called quartz conglomerate. Take a closer look at the rock surface at the base of the cliff and some of the many rock pieces littering the ground in the surroundings. What is the size of the quartz pebbles in the stone?
2. Pick one of the conglomerate rock pieces from the ground - find one compact and not cracked. Try to break it using your hammer (or use another piece of rock). Be careful not to hurt yourself or someone near you.
2.a: Is this conglomerate soft? Is it easy to break it?
2.b: What do you think - what was the main product of this quarry: White or Black millstones? Your findings from previous task (2.a) may help you to answer.
3. Cliff is not uniformly coloured. Which shades prevail? What, in your opinion, is the reason for this this colouring?
4. NOT OBLIGATORY: Find one especially interesting item in the quarry: You can see a »draft« of the millstone somewhere at the cliff – an unfinished millstone, almost completely shaped but left there. See Image 3 (or image at info board) for help.
4.a: Where in the quarry is the unfinished millstone located? Write down coordinates when you find it.
4.b: Measure the height from the ground to the lower edge of the unfinished millstone.
4.c: Measure the distance of the unfinished millstone from the EarthCache coordinates (info board).

- Send answers through GC profile or directly to e-mail
before logging. After that you can log - you don't need an additional permission to log. Please, upload photos if you have taken them.
- Logs without an accompanying e-mail containing correct answers will be encrypted and later deleted!
- Logs containing answers will be deleted!

slovensko besedilo / Slovenian text
tocke poti in dnevniki / waypoints and logs

Visit our web-site Geološki zakladi / EarthCaches
for a complete list of our EarthCaches and a lot of additional information.

Stone is one of the most important materials we people use for many different purposes. It has become irreplaceable in the process of flour production ever since the spread of the agriculture. Artificial stones started to replace natural millstones in the 19th century. And even those still used sand as main material. Ease of manufacturing and lower prices of artificial millstones heralded the slow but definite decline of handmade stone-cut millstones. By now, artificial millstones have also been replaced at flour production - with roller mills.

Conglomerate rocks have been the usual choice for the production of millstones. Conglomerate is a detrital sedimentary rock. In other words, it is a rock consisting of many individual rounded gravel pieces – from large (as boulders) to small pebbles (the size of garden peas) which have become bound together. It happens after the gravel layers are buried beneath younger layers - they are slowly compacted and cemented together – it takes eons. The »glue« or binding material could be mineral cement (quartzite or calcite) which is crystallized from the water solution, or fine-grained matrix (clay, sand) or both.

Image 1: Conglomerate rocks from Kokra river valley and location Stari grad (Podgrad). Pebbles in these samples are quartz; photo: Vane.

Sedimentary rocks are prevailing type of bedrock in Slovenia. White millstones have been mainly produced from softer and brighter white-to- grayish limestone conglomerates (conglomerates consisting mainly of limestone gravel). Black millstones, on the other hand, were made from harder and darker brown-to-grayish quartz conglomerates. The distinction between »white« and »black« millstones, however, doesn't come from the colors of stones, but from the different types of flour which the millstones were used for. White millstones have been used for milling wheat, corn, buckwheat, and grain mixtures. Black millstones have been used to mill oats, barley, coarse ground oats, and corn-barley mixtures for pigs.
Many of the former quarries in Europe are protected as cultural heritage today. Only a few are preserved in Slovenia. One of them is the Podgrad quarry, at the eastern outskirts of Ljubljana.

Podgrad is a village settled at the mouth of Besnica stream, just a stone's throw from Zalog and confluence of three rivers – Sava, Ljubljanica and Kamniška Bistrica. At the pointy hilltop in the ridge of Kašeljski hrib (Kašelj hill) which rises in the southwest of the village, ruins of medieval castle stand. The hilltop used to be called Ostri vrh (literally »Pointy hilltop«), and is now known as Stari grad (the Old Castle). There is a sandstone and conglomerate rock cliff at the step southern hillside, just below the Old Castle. This cliff is roughly 40 meters wide and 25 meters high. There are several smaller cliffs in the surroundings which bear clear marks of curved stonecutting. The production of millstones is documented there. The rocks have been determined as quartz conglomerate from Perm-Carbon period (small pieces of quartz in the quartz-sand matrix).

Image 2: Location of Podgrad village, Stari grad Castle (yellow dot) and millstones quarry (red dot).

Some documents about stonecutters »from beneath Ostri vrh« and about quarry existence are preserved. The oldest document, discovered so far, is reference in the probate proceedings after the late lord Jurij Galenberg, from the year 1567. Next is the reference from 1611 which mentions that »... they have made three pairs of millstones for the Ljubljana municipal mill Kolezija in this quarry, and have been paid 21 goldinar (gulden)«. There is one more document from 1617 and reference to the quarry in the1666 land registry of Ostri vrh and Dol.
It is unknown when the quarry started to operate, but it has been definitely very long time ago. It is not unlikely that Romans have used it already – their settlements used mills to grind grain, they also had iron tools for stonemasonry.
It is estimated that several thousand millstones have been made in this quarry. And one more interesting data: skilled stonecutter needed about one week to finish one millstone wtih his hand toos.

Image 3: Podgrad millstones quarry: one of the cliffs with clear stonecutting marks. An unfinished millstone, left in the cliff; photo: Vane.

Marked trail “Ostrovrharjeva pot” leads past millstones quarry. Access is possible uphill from the direction of Besnica stream, and downhill from Stari grad (Old Castle).
Here is the short descripton of access from Besnica stream: Park your car at waypoint PARKNG, cross wooden bridge and follow footpath southwards. Turn your back to the stream at waypoint R1 and follow wide trail leading uphill. You will pass waypoint R2 with a small quarry. Continue ascend to EarthCache coordinates in the quarry. As you look at the cliffs you can easily see lots of circle-like-shaped cutting marks, proof that many millstones have been taken from there.
Information board at the EarhtCache coordinates is in Slovene only, but you’ve got more information in this description already. Follow the path through quarry and a little bit further uphill (to northeast), since the quarry encompasses more separated parts of the cliff. Footpath would also lead you to the summit and ruins of the Old Castle – not far away.

Note: You use trails at your own risk. Use only trails you are fit to. Be safe and enjoy!
We recomend walking sticks for trail and a hammer for one of the tasks.
- Smerdel, Inja, 2006, Ljubljana, Etnolog magazine, Studies: Kamni, ljudje in voli? (Stones, people, and oxen?);
- Lutgens, F.K. et. al.,2012, USA, Essentials of Geology, eleventh edition;
- Information board at the quarry;
- relief and topo map are taken from web-atlas Geopedia,

Slovensko besedilo

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Kamen je od nekdaj pomembno gradivo, ki ga ljudje uporabljamo za mnogo raznovrstnih namenov. Vse od razširitve poljedeljstva je bil nepogrešljiv v postopku predelave žitnega zrnja v moko. V 19. stoletju so mlinske kamne iz naravnega kamna postopoma pričeli zamenjevati mlinski kamni iz umetnega kamna. Pa še pri teh je kot polnilo običajno uporabljen drobljen naravni kamen. Umetni mlinski kamni so pomenili počasen a zanesljiv zaton kamnoseškega izdelovanja. Danes tudi umetne mlinske kamne v veliki meri nadomeščajo mlinski valji in drugačni načini mletja moke.

Za izdelovanje mlinskih kamnov so običajno uporabljali konglomeratne kamnine. Strokovno povedano, je konglomerat debelozrnata klastična sedimentna kamnina, sestavljena iz klastov ali odlomkov, ki nastanejo pri preperevanju in eroziji starejše kamnine in jih voda obrusi v prodnike. Bolj preprosto to pomeni, da je konglomerat mehanska usedlina, ki nastane iz koščkov (na različne načine) razpadlih starejših kamnin, ki jih vodni tokovi odnesejo, kotalijo po dnu struge in trkajo med seboj, zmanjšajo in obrusijo v prodnike. Prod (sestavljen iz množice različno velikih prodnikov in vmes ležečega peska) se preko stoletij in tisočletij zgoščuje in prične s pomočjo veziva sprijemati. Vezivo je lahko mineralni cement (pogosto kremenov ali kalcitni), ki se izloča iz vodne raztopine, ali drobnozrnata osnova (peščena, glinena ali lapornata), ali pa oboje.

Slika 1: Konglomerat iz doline Kokre in kamnoloma pod Starim gradom (Podgrad). Prodniki v teh vzorcih so kremenovi; foto: Vane.

V Sloveniji je kamninska podlaga pretežno iz usedlin (sedimentnih kamnin). Za izdelovanje belih mlinskih kamnov so, kot kaže, povečini uporabljali mehkejše in svetlejše, belkasto sivkaste apnenčeve konglomerate, oziroma konglomerate s pretežno apnenčevimi prodniki. Za klesanje črnih mlinskih kamnov pa trše in temnejše rjavkasto sivkaste kremenove konglomerate. Poimenovanje na »bele« in »črne« kamne je bolj vezano na vrsto moke, ki so jo z njimi pridobivali, kot pa na kamnino iz katere so bili izdelani. Bele mlinske kamne so uporabljali za mletje pšenice, koruze, ajde in zmesi več žit, črne za oves in ječmen ter bolj grobe ovsene, koruzne in ječmenove zmesi za prašiče.
Danes so mnogi od nekdanjih kamnolomov mlinskih kamnov po Evropi zavarovani kot kulturna dediščina. Pri nas je ohranjenih le malo. Eden najlepše ohranjenih je kamnolom Podgrad, le streljaj od Ljubljane.

Vas Podgrad pri Ljubljani se je umestila ob izlivu potoka Besnica v Ljubljanico, le za lučaj od Zaloga in tik pred sotočje Save, Ljubljanice in Kamniške Bistrice. Na jugozahodu se nad njo dviga Kašeljski grič, kjer na zašiljenem stranskem vrhu z nekdanjim ledinskim imenom Ostri vrh (Oster verh), na današnjem Starem gradu, leže ruševine srednjeveškega gradu rodbine Ostrovrharjev. Prav pod njim, malo pod vrhom vzpetine in južno od ruševin, je v strmem in skalovitem pobočju navpičen odlom peščenjaka, oziroma konglomerata, višine okoli 25 metrov in širine 40 metrov. V bližini se nahaja še več manjših pečin s krožnimi sledovi klesanja. V njih je izpričano dolgoletno izdelovanje mlinskih kamnov. Kamnino je bilo mogoče določiti kot permokarbonski kremenov konglomerat - majhni prodniki kremena s kremenovo-peščenim vezivom.

Slika 2: Lega Podgrada, Starega gradu (rumena pika) in kamnoloma (rdeča pika).

O dejavnosti starodavnih mlinskih kamnosekov izpod Ostrega vrha, oziroma o obstoju kamnoloma, pričajo nekateri dokumenti. Najzgodnejša doslej odkrita omemba je v zapuščinski razpravi po graščaku Juriju Galenbergu (Ostrovrharju) iz leta 1567. Naslednja je omemba iz leta 1611, da »so v njem za 21 goldinarjev izdelali tri pare mlinskih kamnov za ljubljanski mestni mlin Kolezija«. Obstaja še zapis o dobavi kamnov iz tega kamnoloma iz leta 1617 in navedba kamnoloma v urbarju Ostrega vrha in Dola iz leta 1666 (Grilc 2003: 71).
Začetek delovanja kamnoloma ni znan, je pa časovno zelo oddaljen, morda vse do rimskih časov. Rimska naselja (1. do 5. stoletje n.š.) so bila blizu in so imela mline. Imela so tudi železna orodja za obdelavo kamna. Zato je možno, da so bili prvi kamnoseki tu prav Rimljani.
Ocenjeno je, da so iz tega kamnoloma izklesali več tisoč mlinskih kamnov. Pa še ena zanimivost: izurjen kamnosek je za izdelavo enega mlinskega kamna z ročnim orodjem potreboval teden dni.

Slika 3: Kamnolom Podgrad (pod Starim gradom): ena od skalnih sten z jasnimi sledovi dela kamnosekov. Nedokončan mlinski kamen puščen v steni kamnoloma; foto: Vane.

Mimo kamnoloma vodi označena in obiska vredna, krožna Ostrovrharjeva pot. Dostop je možen po poti od potoka Besnice navzgor ali med spustom po stezi od Starega gradu.
Tu je kratek opis dostopa od potoka Besnica: Avto pustite na točki PARKNG, po mostu prečkate potok Besnica in nadaljujete po stezi proti jugu – to je del Ostrovrharjeve poti, ki sicer »uradno« vodi v nasprotno smer. Pri točki R1 široka pot zavije strmo v hrib. Tej poti sledite mimo točke R2 (manjšega kamnoloma) do koordinat Geološkega zaklada, ki so pri informacijski tabli. Stene kamnoloma so bogato zaznamovane s krožnimi sledovi izsekavanja, ki jasno kažejo na pridobivanje grobih kosov za mlinske kamne. Sledite stezi skozi kamnolom in še nekoliko naprej (proti severovzhodu), saj kamnolom obsega več ločenih delov stene. Steza vas nad kamnolomom kmalu pripelje povsem do vrha grebena, k ruševinam Starega gradu.

Opombe: Poti uporabljate na lastno odgovornost! Hodite le po poteh za katere ste ustrezno pripravljeni! Zelimo vam varno pot in veliko uzitkov!
Za vzpon in spust priporočamo uporabo pohodniških palic.
- Smerdel, Inja, 2006, Ljubljana, revija Etnolog, Razprave: Kamni, ljudje in voli?;
- Lutgens, F.K. et. al.,2012, USA, Essentials of Geology, eleventh edition;
- Informacijska tabla v kamnolomu;
- relief in topo karta so povzeti iz spletnega atlas Geopedia,

tocke poti in dnevniki / waypoints and logs

Additional Hints (No hints available.)