Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Friday, May 29, 2009

Flight over the Wollondilly and Nattai Rivers

Several days ago I went for a quick flight with my friend Jim.
He wanted to go west, over the Wollondilly River, to show me a particular geographical feature he had seen on a trip back to his home from Cowra.
We flew just south of Bowral - towards Mt Jellore, which is west of Mittagong, and north of the Wombeyan Caves Road (at High Range). Mt Jellore is a near perfect cone which stands high above the horizon in this view (above where I have written its name). (Click to enlarge image)

Unfortunately, the weather was against us, when we got out towards the Wollondilly River, near Bullio. We circled around to see the clifflines and obvious hills out there, but many features could not be seen because of low cloud.
Here is the Wollondilly Valley, with a cliff line from near Mt Wanganderry
which is the highest point on the High Range, along the Wombeyan Caves Road.
Here is Mt Jellore, seen from close above.
This contour map image shows well how round this mountain is.
It is over 800 metres high, rising out of the Nattai Valley and Wollondilly Valley.

The weather was against us, but what could be seen was pretty wild, and invites further examination - by 4 wheel drive vehicle, and on foot.
This remarkable cliff formation is extremely narrow.
Without checking for names on detailed contour maps, I don't know if it has an official name.
I have referred to it as the Knife Edge Cliff, beyond Mt Jellore.
Even Jim was impressed with it, and graciously allowed another fly past, for me to get this shot.
It looks like a natural spot to find Peregrine Falcons, to me.
Wonderful clifflines.


mick said...

That sounds such a great flight over extremely interesting country. Would Mount Jellore be the eroded cone of a volcano? And would an uplift have made that knife-edge cliff? (Uh-oh! Hope I have remembered some of the right words! Hope you understand what I am asking!)

Miss Eagle said...

Perhaps eagles fly at the Knifedge too, Denis?

Denis Wilson said...

Hi Mick
Sorry for the slow response.
Yes, it is almost certainly a basalt plug. There are a number of them in the region. Old volcanoes which developed a flow which leaves behind a pimple of hard rock. From a volcano which was not so hot as to explode, like Mt Warning, or the nice ones in western Victoria which have a crater lake inside their little cones.
I could not find a geological map on the web to show that for sure. Certainly the rock type looks different in the images from the sandstone in the knife edge promontory, which is classic sandstone, eroded by two rivers - one on either side.
The rocks in Mt Jellore are not laid down in strata (as you can see in the close up shot of the "Knife Edge Cliff"). Those rock on Mt Jellore are more likely in a vertical alignment, more or less like columns or tubes of frozen lava. These are lava protrusions up through the much older sandstone strata, which occurs when a "hot spot" develops underneath the sandstone.
Mt Jellore is probably the last in a line of such small volcanic protrusions, starting from near Robertson, some 60 Km east. They left a ridge, with some free standing hills. Mt Jellore is the most isolated in out area - the volcano's last gasp, as it were.

Denis Wilson said...

Hi Miss Eagle.
Certainly it is great Eagle country in there. You have seen images of Eagles flying near Bullio, in the same area, overlooking the Wollondilly River.
But I mentioned Peregrines because they nest on cliffs like the Knife Edge.

Jack Hinde said...

Your "Knife edge" is a feature known as Russell's Needle. It is a thin sandstone wedge similar in geology to the 3 sisters, and also to the Bonnum Pic, which is the feature on the right side of your second image. I have climbed Russells Needle, Bonnum Pic and Mt. Jellore each a few times.
Incidently, Jellore is not Basalt, and like its microsyenite sister the Gib, was never an active volcano, merely a magma intrusion. Mt Wangaderry to the south is basalt similar to the lava flows of Robertson.

Denis Wilson said...

Thanks Jack for your expert information.

To non-Geologists like me, it is always good to get the "background" to the different features of this region.

I shall have to check out "microsyenite" further - not a term with which I am familiar.



Jonathan Berry said...

Microsyenite or Trachyte is common to both Mt Jellore and Mt Gibralter at Mittagong. On the Bowral side of the Gib there is a quarry (now closed). The Trachyte from here was taken to Sydney and is the familiar hard blue curb stone found on every street throughout the CBD. This stone was much more durable than the common Hawkesbury sandstone which is porous and soft.

If I recall correctly, the sandstone ridges surrounding Mt Jellore have been laid much more recently than the igneous cone as part of a more recent ancient seabed.

Denis Wilson said...

Thanks Jonathan for the technical information.
Much appreciated.
I do better on Orchids than on rocks.
But I do like to cover the bigger pictures where I can.
Expert information like yours helps.

Jonathan Berry said...

Thanks Denis, Not actually an expert and went out on a limb with the point about the surrounding ridges being a more recent system than the Hawkesbury system.

It is just that the "Volcano" happens to be at the bottom of my

Denis Wilson said...

Well, Jonathan, that makes you well qualified to comment!
If you ever organise a trip there, I would love to know.
My email address is on my profile page.
I have tried to find my way into some of that rough country, but have never got to the foot of Mt Jellore.
My main interests are in the plants, and I know that the Nattai region has many interesting things.
Edge country - change-over points between habitats - are full of surprises.
Denis Wilson