diff --git a/src/worldgen/DensityFunction.ts b/src/worldgen/DensityFunction.ts
index 2e4feacf..9384e310 100644
--- a/src/worldgen/DensityFunction.ts
+++ b/src/worldgen/DensityFunction.ts
@@ -88,8 +88,8 @@ export namespace DensityFunction {
 			case 'find_top_surface': return new FindTopSurface(
 				inputParser(root.density),
 				inputParser(root.upper_bound),
-				Json.readNumber(root.lower_bound) ?? 0,
-				Json.readNumber(root.cell_height) ?? 1,
+				Json.readInt(root.lower_bound) ?? 0,
+				Json.readInt(root.cell_height) ?? 1,
 			)
 			case 'weird_scaled_sampler': return new WeirdScaledSampler(
 				inputParser(root.input),
diff --git a/src/worldgen/NoiseChunk.ts b/src/worldgen/NoiseChunk.ts
index a7419f5c..560302da 100644
--- a/src/worldgen/NoiseChunk.ts
+++ b/src/worldgen/NoiseChunk.ts
@@ -15,10 +15,10 @@ export class NoiseChunk {
 	public readonly firstNoiseX: number
 	public readonly firstNoiseZ: number
 	public readonly noiseSizeXZ: number
-	private readonly preliminarySurfaceLevel: Map<bigint, number> = new Map()
+	private readonly preliminarySurfaceLevelCache: Map<bigint, number> = new Map()
 	private readonly aquifer: Aquifer
 	private readonly materialRule: MaterialRule
-	private readonly initialDensity: DensityFunction
+	private readonly preliminarySurfaceLevel: DensityFunction
 
 	constructor(
 		public readonly cellCountXZ: number,
@@ -51,7 +51,7 @@ export class NoiseChunk {
 		this.materialRule = MaterialRule.fromList([
 			(context) => this.aquifer.compute(context, finalDensity.compute(context)),
 		])
-		this.initialDensity = randomState.router.initialDensityWithoutJaggedness
+		this.preliminarySurfaceLevel = randomState.router.preliminarySurfaceLevel
 	}
 
 	public getFinalState(x: number, y: number, z: number): BlockState | undefined {
@@ -59,16 +59,11 @@ export class NoiseChunk {
 	}
 
 	public getPreliminarySurfaceLevel(quartX: number, quartZ: number) {
-		return computeIfAbsent(this.preliminarySurfaceLevel, ChunkPos.asLong(quartX, quartZ), () => {
+		return computeIfAbsent(this.preliminarySurfaceLevelCache, ChunkPos.asLong(quartX, quartZ), () => {
 			const x = quartX << 2
 			const z = quartZ << 2
-			for (let y = this.settings.minY + this.settings.height; y >= this.settings.minY; y -= this.cellHeight) {
-				const density = this.initialDensity.compute(DensityFunction.context(x, y, z))
-				if (density > 0.390625) {
-					return y
-				}
-			}
-			return Number.MAX_SAFE_INTEGER
+
+			return Math.floor(this.preliminarySurfaceLevel.compute(DensityFunction.context(x, 0, z)))
 		})
 	}
 }
diff --git a/src/worldgen/NoiseRouter.ts b/src/worldgen/NoiseRouter.ts
index 2c91b946..242ddb9a 100644
--- a/src/worldgen/NoiseRouter.ts
+++ b/src/worldgen/NoiseRouter.ts
@@ -16,7 +16,7 @@ export interface NoiseRouter {
 	erosion: DensityFunction,
 	depth: DensityFunction,
 	ridges: DensityFunction,
-	initialDensityWithoutJaggedness: DensityFunction,
+	preliminarySurfaceLevel: DensityFunction,
 	finalDensity: DensityFunction,
 	veinToggle: DensityFunction,
 	veinRidged: DensityFunction,
@@ -39,7 +39,7 @@ export namespace NoiseRouter {
 			erosion: fieldParser(root.erosion),
 			depth: fieldParser(root.depth),
 			ridges: fieldParser(root.ridges),
-			initialDensityWithoutJaggedness: fieldParser(root.initial_density_without_jaggedness),
+			preliminarySurfaceLevel: fieldParser(root.preliminary_surface_level),
 			finalDensity: fieldParser(root.final_density),
 			veinToggle: fieldParser(root.vein_toggle),
 			veinRidged: fieldParser(root.vein_ridged),
@@ -59,7 +59,7 @@ export namespace NoiseRouter {
 			erosion: DensityFunction.Constant.ZERO,
 			depth: DensityFunction.Constant.ZERO,
 			ridges: DensityFunction.Constant.ZERO,
-			initialDensityWithoutJaggedness: DensityFunction.Constant.ZERO,
+			preliminarySurfaceLevel: DensityFunction.Constant.ZERO,
 			finalDensity: DensityFunction.Constant.ZERO,
 			veinToggle: DensityFunction.Constant.ZERO,
 			veinRidged: DensityFunction.Constant.ZERO,
@@ -80,7 +80,7 @@ export namespace NoiseRouter {
 			erosion: router.erosion.mapAll(visitor),
 			depth: router.depth.mapAll(visitor),
 			ridges: router.ridges.mapAll(visitor),
-			initialDensityWithoutJaggedness: router.initialDensityWithoutJaggedness.mapAll(visitor),
+			preliminarySurfaceLevel: router.preliminarySurfaceLevel.mapAll(visitor),
 			finalDensity: router.finalDensity.mapAll(visitor),
 			veinToggle: router.veinToggle.mapAll(visitor),
 			veinRidged: router.veinRidged.mapAll(visitor),
diff --git a/test/worldgen/DensityFunction.test.ts b/test/worldgen/DensityFunction.test.ts
index d1fcfc4e..ebeb1934 100644
--- a/test/worldgen/DensityFunction.test.ts
+++ b/test/worldgen/DensityFunction.test.ts
@@ -2,8 +2,8 @@ import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import { Holder } from '../../src/core/Holder.js'
 import { Identifier } from '../../src/core/Identifier.js'
 import { CubicSpline, NoiseParameters } from '../../src/math/index.js'
-import { DensityFunction as DF, NoiseGeneratorSettings, NoiseRouter, WorldgenRegistries } from '../../src/worldgen/index.js'
 import { RandomState } from '../../src/worldgen/RandomState.js'
+import { DensityFunction as DF, NoiseGeneratorSettings, NoiseRouter, WorldgenRegistries } from '../../src/worldgen/index.js'
 
 describe('DensityFunction', () => {
 	const DELTA = 1e-7
@@ -107,6 +107,13 @@ describe('DensityFunction', () => {
 		expect(fn3.compute(ContextA)).toEqual(-0.33570833333333333)
 	})
 
+	it('Invert', () => {
+		const fn1 = wrap(new DF.Mapped('invert', new DF.Constant(2)))
+		expect(fn1.compute(ContextA)).toEqual(0.5)
+		const fn2 = wrap(new DF.Mapped('invert', new DF.Constant(0)))
+		expect(fn2.compute(ContextA)).toEqual(Number.POSITIVE_INFINITY)
+	})
+
 	it('Add', () => {
 		const fn1 = wrap(new DF.Ap2('add', new DF.Constant(2), new DF.Constant(3)))
 		expect(fn1.compute(ContextA)).toEqual(5)
@@ -177,4 +184,13 @@ describe('DensityFunction', () => {
 		expect(fn2.compute(DF.context(0, 128, 0))).toEqual(0)
 		expect(fn2.compute(DF.context(0, 129, 0))).toEqual(0)
 	})
+
+	it('FindTopSurface', () => {
+		const fn1 = wrap(new DF.FindTopSurface(new DF.YClampedGradient(128, -128, -1, 1), new DF.Constant(128), -128, 1))
+		expect(fn1.compute(ContextA)).toEqual(-1)
+		const fn2 = wrap(new DF.FindTopSurface(new DF.YClampedGradient(128, -128, -1, 1), new DF.Constant(-20), -128, 1))
+		expect(fn2.compute(ContextA)).toEqual(-20)
+		const fn3 = wrap(new DF.FindTopSurface(new DF.YClampedGradient(128, -128, -1, 1), new DF.Constant(50), 128, 1))
+		expect(fn3.compute(ContextA)).toEqual(128)
+	})
 })