Unusual Sandstone Formations

Earth, , ,

There’s no shortage of sandstone in the Sydney area, almost the entire extent of Garigal National Park sits on whats known as the Hawkesbury Sandstone. The Sydney 1:100 000 Geological Sheet classifies it as “Medium to course-grained quartz sandstone, very minor shale and laminite lenses” I wanted to highlight two sandstone formations, both of which are a bit of a mystery as to how they form.

I came across these formations on a trail run on a section of single track in Belrose that runs from the end of Ralston Ave down to the Bare Creek trail next to Bare Creek.

The first formation is called tessellated pavement.

tessellated pavement on the trail down from Ralston Ave to Bare Creek. Shoe for scale

There are a number of different types of tessellated pavement. The type I came across is seen on flat sections of sandstone that have been fractured into 4-6 sided geometric shapes. Some of the blocks are surrounded by deep grooves with rounded edges. It really looks like a man made road or path the way the blocks lock together. It’s not known how this structure forms.

The second formation is even more of a mystery.

Grooves and ridges on the trail. Is it rundkarren in sandstone?
The same formation with shoe for scale

It was on the same section of trail near the tessellated pavement. Found on a gently sloping section of sandstone, it had rows of deep grooves all running in the same direction from the top of the slope to the bottom. They looked like they could have been worn over many years by the trickle of water. Above the trail was a minor gully, there wasn’t any visible creek but it looked damp and swampy. In wetter times perhaps water could have drained slowly over the sandstone. This is all guessing, I couldn’t find any information on this type of formation. The closest I came was rillenkarren or rundkarren which is the weathering of similar channels in limestone by the slight acidity of the water dissolving the rock. Rillenkarren has sharper ridges and is thought to form out in the open while rundkarren is more rounded and thought to form under a superficial covering like sandy till, peat or a layer of plants and lichen.

Wikipedia

British geological survey

Speliogenisis

One Mans Funnies

Holes and burrows in sandstone

Animals,

In the bush nearby you can often see sections of sandstone that have clusters of regular sized holes around 10mm in diameter. Sometimes these pieces of sandstone are on a walking track where they get worn down to show the internal paths these holes take. I have a distant hazy memory of being told the holes are made by native bees. A bit of the old web searching brought up some more information!

Holes in sandstone with $5 note for scale. This was taken in the upper sections of Carroll Creek near Forestville
This piece of sandstone was part of the track and has been worn down by the tread of many feet. It reveals the paths the burrows take. Sneaker toe for scale. The location of the photo is just above Berowra creek out the back of Westleigh

The holes in sandstone are apparently the burrows of a native bee called the Blue Banded Bee. Blue Banded bees are found all over Australia except Tasmania and the Northern Territory. They are solitary bees that build their nests in mud and soft sandstone, they are also known to burrow into the mortar of old buildings.

I’ve not seen one of these bees myself so I don’t have a picture. They are described as being 8mm – 13mm long with a furry red brown thorax and blue and black stripes on it’s abdomen. They live around 40 days, baby bees remain in their eggs over winter but several generations can hatch over the warmer months. They are meant to be common, I’ll be keeping an eye out to try and get a picture.

[update] – Found some!

Spider wasp catching a spider

Animals,

It was over a year ago that I first saw this flying insect that had caught a large spider and was dragging it off somewhere presumably to eat. I’d never seen anything like it and I spent a while researching to try and work out what it was. At the time I thought it was a robber fly but now I think it’s a spider wasp!

Robber flys do indeed prey on some spiders and other insects but the images really dont look anything like what I’d seen.

The spider wasp is a much closer match. I’ve seen a few now, here’s some pictures of a smaller spider wasp with another decent sized spider. This particular one was struggling a bit with it’s prey. It even tried to fly a bit and only just managed it. Looking at the picture the spider could easily weigh more than the wasp!

Spider wasps are known to chop off the legs of the spider to make it easier to carry. All the ones I’ve seen the spiders are missing their legs. Nature is brutal!

Spider Wasp
Spider Wasp with a big spider. Spider wasps are known to remove the spiders legs to make them easier to carry

Resources and References

Have you ever seen a fly catch a spider?

Animals, , ,

[update] – When I wrote this I thought the creature was a robber fly, now I think it’s a spider wasp.

Here’s something you don’t see every day, a large fly like creature walking along carrying a sizeable spider underneath it! Now that’s a prey reversal! A bit like seeing a huge rat hauling a dead cat somewhere.

The fly was black, about 4cm in length with long legs that allowed it to carry the spider underneath it and still walk easily. The one I saw was on a mission to get somewhere, it walked quickly over the pavement for about 4m and then climbed a wall before I lost it. It had wings but didn’t try to fly, maybe the spider was too heavy for it. The spider was slightly longer than the fly and looked bulkier, all the spiders legs were gone and it was being carried inverted with it’s abdomen towards the front of the fly.

I think this is a robber fly, it’s somehow caught a large spider and is hauling it off somwehere

Curious as to if this was normal I did some searching. The closest thing I could find that lives in the area is a robber fly. “Robber flies are large, bristly flies that catch their prey (usually other insects) mid-flight.” Robber flys are known to catch and eat spiders, the fly I saw didn’t have the same enlarged powerful chest as the robber fly photos on the articles. It looks like there is some variation between robber fly species so maybe it’s just a different species that I saw.

It was moving fast and I only had my phone on me so I found it hard to get a clear picture, but you can see the size of the spider compared to a garden hose and a house brick. The spider looked like a huntsman, I’m not sure how the fly would have killed it and removed it’s legs, or maybe it found the spider like that?

Fly hauling a large spider away somewhere

Fly hauling a large spider. Garden hose for scale, shame the subject is blury

Resources and references